Amps to watts: formula and table for converting current to power and vice versa

On household appliances (mixer, hair dryer, blender), manufacturers write the power consumption in watts, on devices that require large amounts of electrical load (electric stove, vacuum cleaner, water heater) - in kilowatts. And on sockets or circuit breakers through which devices are connected to the network, it is customary to indicate the current strength in amperes. To understand whether the outlet will support the device you are connecting, you need to know how to convert amps to watts.

Is there a difference between Volts and Watts?

First, let's remember what these concepts mean.
Let’s also try to find out if there is a significant difference between them. So, an electrical voltage that produces a current whose strength is equal to 1 Ampere is called a Volt. In this case, it stands in a conductor with a resistance of 1 ohm.

Volts can be divided:

  • 1,000,000 microvolts
  • 1,000 millivolts

At the same time, we can say that Watt is the constant power of electric current. At a voltage of 1 Volt, its power is 1 Ampere.

Based on the above, we can safely say that there is still a difference between these concepts. Therefore, it must be taken into account when working with various electrical systems.

How is current measured?

Units of measurement of the main indicators of the electrical network: ampere, watt (kilowatt), volt. In this case, the current strength is measured in amperes and shows the speed of charge passing through the conductor over a certain period of time.

Instruments for measuring current strength

The current strength of the electrical network is measured by a special device - ammeter . The type of equipment depends on the network voltage (DC or AC). The data obtained is used to determine the maximum load on the wiring, as well as to calculate the rated and actual power of the electrical appliances used.

What is current (Ampere [A])

It is important for the user to calculate the rated current of the electrical network in advance. The choice of cross-section of the wiring cores, as well as the equipment of the safety circuit breaker, depends on this.

What is voltage (Volt [V])

The concept of “voltage” includes the energy required to move an electric charge over a certain distance in a specified period of time. This indicator is measured in volts.

What is power (Watt [W])

The power indicator determines the rate of energy consumption over a certain period of time. Power is measured in watts or kilowatts , but there is also the concept of kilowatt/hour , according to which all consumers are charged for the electricity actually used.

Typically, manufacturers indicate the power consumption of electrical appliances (watts, kilowatts) , it can be seen on the packaging or product data sheet. When connecting powerful equipment, it is also important to calculate a sufficient reserve of sockets or machines, the parameters of which are measured in amperes. To connect safely, it is important to understand the difference between these concepts and be able to quickly convert amps to watts and vice versa. Using the online calculator on our website, you can do this in a matter of seconds.

How many volts does 1 ampere contain?

It is quite difficult to answer this question. However, to make it easier for you to understand this issue, we suggest that you familiarize yourself with the tables of ratios:

For DC:

  1. Volts
W: A = A x Ohms = √ (W x Ohms)
Amps(W : V) = √(W : Ohms) = V : Ohms
OhmsB : A = W : (A)2 = (B)2 : W
WattsA x B = (A)2 x Ohms = (B)2 : Ohms

For AC:

VoltsW: (A x cos Ψ) = A x Ohms x cos Ψ = √(W x Ohms)
AmpsW: (V x cos Ψ) = 1/cos Ψ x √(W: Ohms) = V: (Ohms x cos Ψ)
OhmsB : (A x cos Ψ) = W : (A)2 • cos2 Ψ = (B)2 : W
WattsB x A x cos Ψ = (A)2 x Ohms x cos2 Ψ = (B)2 : Ohms

Converting power units by dividing by voltage, converting with a calculator

To select a circuit breaker, use the following formulas:

  • direct current (single-phase network 220 V ):

I = P/U,

  • three-phase network 380 V :

I = P/ (U * √3).

The data obtained will be useful for selecting wiring, sockets, and other functional components.

Ampere calculator

For your information. On specialized websites you can find a Watt calculator and other programs for automated calculations.

What are Volt Amperes and how to convert them to Watts?

Another unit of measurement of power adopted in SI is Volt-ampere (VA). It is equal to the product of effective values ​​such as current and voltage.

Additionally, it is worth noting that, as a rule, VAs are used solely to estimate the power in AC connections. That is, in cases where Watt and Volt-Ampere have different meanings.

There are now many different online calculators that allow you to quickly and easily convert VA to Watts. This procedure is so simple that we will not dwell on it.

But, especially for those people who do not have an online calculator at hand to convert Volt-amps to Watts, we will look at the process of converting these quantities in more detail:

  1. Energy is produced or consumed at a certain rate. And Watt is one of the units of power.
  2. To measure the magnitude of the electric current, A is used, which is equal to 1 Coulomb.
  3. Electromotive force or voltage is measured in Volts.
  4. In order to remember how these quantities relate to each other, you need to learn the following formula: Amps = Watts/Volts

Using this formula we can find out the current strength. Of course, only if we already know the voltage and power.

That is, it turns out that to convert Watts to Amperes, we must find out the voltage in the system. For example, in the USA the voltage in the electrical network is 120V, and in Russia it is 220V.

It is worth noting that batteries used in cars usually have a voltage of 12 V. And the voltage in small batteries used for various portable devices, as a rule, does not exceed 1.5 V.

Thus, we can say that knowing the voltage and power, we can easily find out the current strength as well. To do this, we only need to correctly use the above formula.

Let's look at how this “works” with a specific example: if the voltage is 220V and the power is 220W, then the current will be 220/220 or 1 A.

What is the difference between ampere and kilowatt

The fundamental difference between the units of measurement of electrical network parameters, which are included in the title of this section, is that they represent a numerical measure of various physical quantities.

In this case:

  • amperes (abbreviation A) show current strength;
  • watts and kilowatts (abbreviation W and kW, respectively) characterize active (actually useful) power.

In practice, an expanded description of power is also used, measuring it in volt-amperes and, accordingly, kilovolt-amperes, which are briefly referred to as VA and kVA.

They, unlike W and kW, which describe active power, indicate total power.

In DC circuits, the apparent and active powers are the same. Similarly, in an AC network, with a small load power, at the engineering level of rigor, the difference between W (kW) and VA (kVA) can be ignored, i.e. work only with the first two units.

For such circuits the following simple relation applies:

W = U*I, (1)

where W is the (active) power specified in W, U is the voltage specified in volts, I is the current measured in amperes.

When the load power increases to a level of a thousand watts and above for direct current, relation (1) does not change, but for alternating current it is advisable to write it as:

W = U*I*cosφ, (2)

where cosφ is the so-called power factor or simply “cosine phi”, showing the efficiency of converting electric current into active power.

In physical meaning, φ represents the angle between the vectors of alternating current and voltage or the phase shift angle between voltage and current.

A good criterion for the need to take this feature into account are those cases when VA or kVA are indicated instead of kW in the nameplate data and/or on the body nameplates of electrical appliances, mainly powerful ones with a consumption of more than 1 kW.

Typically, for household electrical devices with powerful electric motors (washing machines, dishwashers, pumps and the like) you can set cosφ = 0.85.

This means that 85% of the energy consumed is useful, and 15% forms the so-called reactive power, which continuously transfers from the network to the load and back again until it is dissipated in the form of heat during these transitions.

At the same time, the network itself must be designed specifically for full power, and not for useful power. To indicate this fact, it is indicated not in watts, but in volt-amperes.

As a unit of measurement, the watt (volt-ampere) is sometimes too small, resulting in numbers that are difficult to visually perceive with many digits. Taking this feature into account, in some cases power is indicated in kilowatts and kilovolt-amperes.

For these units the following is true:

1000 W = 1 kW and 1000 VA = 1 kVA. (3).

How many watts are in 1 ampere?

Now let's try to convert Watts to Amps. And for this we need one more formula:


In it, I is A, P is Watt, and U is Volt.

By making a simple calculation using this formula, we can find out how many Watts are in one A.

As we said earlier, there is another way to calculate how many watts are in 1 A. In order to use it, you will need to open an online calculator and enter the power consumption and voltage into it.

Next, you just need to click on the button labeled “calculate” and within a couple of seconds a special program will give you the correct value. By using this method, you will undoubtedly be able to save your time and effort, since you do not have to independently calculate all the indicators using formulas.

Errors when calculating V•A

The ratios of volt amperes and watts for certain types of electrical appliances and devices, for example, light bulbs, are identical. But when talking about computers, watts and V•A will be different, but V•A will always be greater than or equal to watts. The gap is related to power factor (PF), which varies among devices. If you do not take it into account, then when selecting equipment elements an error will be made and they will not fit the main device.

If we consider the choice of a UPS for a personal computer, and on the passport data the rating is indicated in voltamper, this will make it difficult to select a rating in W. When there are no exact indicators of P, do the following - the load data indicated on the nameplate is taken equal to 60% of the V•A indicator of the UPS.

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Online calculator

Additional Information. In order to more accurately determine the data, you can use an online calculator. Some websites provide the user with the required P if they click on the device type, such as TV or desktop. These sites often show graphical charts that make it easy to measure the V•A of various appliances, from refrigerators to computers.

It can be concluded that V•A is an important characteristic for modern electrical devices and equipment. If this indicator is not taken into account when purchasing electrical devices, they will operate in overload mode, which will lead to their premature failure.

What quantities are measured in Amperes and Watts?

The main quantities needed to convert amps to watts are current, whose unit is 1A (ampere), and voltage, whose unit is 1V (volt).

Important! Power for calculations is measured in watts (W), otherwise the result will be underestimated by 1000 times.

If we roughly compare an electrical appliance with a water mill, then the voltage is the height of the dam, the current is the amount of water flowing through the mill wheel, and the power is the amount of ground grain. The higher the dam level or the stronger the flow, the greater the work done (amount of flour).

It is impossible to directly convert these quantities into each other using certain coefficients. Finding out how many watts are in 1 ampere is possible only in individual cases, for which these coefficients have already been calculated and allow for an approximate recalculation.

For more accurate calculations, all three parameters are needed, and in some cases additional data, such as the number of phases, cos(φ) and efficiency.

Tables of ratios of amperes, volts, watts, ohms

To simplify, the main parameters of the electrical circuit are explained using the example of the functioning of a conventional pipeline. The movement of fluid is ensured by the pressure difference. The narrowing (expansion) of the transport route changes the flow resistance accordingly. If necessary, using the listed parameters or experimentally, you can set the pipeline productivity in liters per unit of time.

By analogy with the above description, the potential difference (voltage) ensures the movement of electric charges (current). As the cross-section of the conductor decreases, the electrical resistance increases. Knowing the basic parameters, it is easy to calculate the power consumption of the connected load.

Table for calculating the comfort zone of “electronic” cigarettes

The specified power data corresponds to certain resistance and voltage values. Similar tables are compiled for converting Watts into amperes and other quantities. This example clearly demonstrates the main disadvantages of the tabular form:

  • complexity of processing large amounts of data;
  • discreteness of information provision;
  • limited accuracy.

Graphical representation of basic formulas for calculating electrical parameters

Using calculations, you can convert volts to amperes quickly and accurately.

For your information. As an alternative, an electrical quantity converter is used, which is available for free use on reference and specialized websites on the Internet.

Formula for direct current

To determine power at constant voltage, the following expression is used - P=U•I, where:

  • P (W) – power of the electrical appliance;
  • U (B) – network voltage;
  • I (A) – current consumption.

Using the rules of mathematics known from elementary school, you can perform a conversion to determine voltage and current. These formulas have the following form, allowing you to calculate one unknown parameter with the other two known:

  • current – ​​I=P/U;
  • power – Р=U•I;
  • voltage – U=P/I.

In this form they are used primarily in DC networks. At home, this voltage is used in car wiring, as well as when connecting LED strips and modules.

For single-phase and three-phase networks, a more complex formula is needed. It is necessary to take into account additional parameters.

What is voltage, Volt [V]

How to calculate amperes

By creating a potential difference, they ensure the movement of charges. The unit of measurement is one Volt. This voltage ensures the movement of 1 Coulomb (C) of electric charge between the poles. During this process, work with energy of 1 Joule (J) is performed.

The same value (V) can be represented as the potential difference to release a unit power of 1 W (W) when the current is limited to one ampere. Similarly, it is permissible to use proportions when determining the relationship between voltage and electrical resistance (R). The listed dependencies can be expressed as follows:


The simplest formulas are valid for calculating a DC network. If sinusoidal oscillations are considered, in addition to the amplitude, it is necessary to take into account the corresponding changes in voltage depending on time. The instantaneous value is described as follows:



  • Ua – maximum voltage deviation (amplitude);
  • w – frequency;
  • t – time;
  • ϕ – phase (initial).

For simplified calculations, it is convenient to use the root mean square voltage ( Uc p), which is related to the amplitude value by the following proportion:

Ucр=Ua*(1/√2)≈ Ua*0.707.

Formula for single-phase network

In electrical engineering there is such a concept as active and reactive load. The reactive load is characterized by the consumption of reactive power and is expressed by the coefficient cos(φ) (cosine “phi”). Taking into account the cos(φ) coefficient, the formula by which you can convert Amps to Watts will look like:

In apartment sockets the voltage is not constant, but alternating. In such networks, in addition to active power, there is reactive power. It appears when there is an inductive or capacitive load. The sum of these powers is called total. The parameter that determines the active load component is called cosφ (cosine phi).

Reference! Electrical devices that consume inductive power are electric motors and transformers. Capacitive loads are found only in electronic circuits and power factor compensators.

In order to find out how many watts are in an ampere, the calculation must be made using the following formulas - P=U*I*cosφ, and the current, accordingly, I=P/(U*cosφ). In everyday life, cosine phi is usually not taken into account.

For “household loads” cos(φ) is equal to one – cos(φ) = 1.

It is also not used when calculating devices that consume only active power - electric heating, electric furnace with heating elements, water heater, electric kettle, electric stoves, incandescent lamps and other similar devices.

To understand how to convert Amps to Watts using the formula, you can consider an example:

  • 11.36 Amps = 2500W/220V
  • 6.81 Amps = 1500W/220V
  • 4.54 Amps = 1000W/220V
  • 2.27 Amps = 500W/220V
  • 1.81 Ampere = 400W/220V
  • 1 Ampere = 220W/220V
  • 0.45 Ampere = 100W/220V
  • 0.27 Ampere = 60W/220V

If we take a 12-volt car battery as an example, a load of 1 ampere will correspond to a power of 12 watts. For a household network with a voltage of 220 Volts, a current of 12 Amps corresponds to 2640 Watts or 2.64 kW.

Conversion table from Volt-amps to Watts

Power losses when connecting a certain load are determined by the correction factor cos ϕ. With linear parameters (incandescent lamps, heating elements), the energy is almost completely used for useful work. In electric motors, reactive components degrade performance characteristics.

The cos ϕ is indicated in the accompanying documentation:

  • 0.6-0.7 – worst indicators;
  • 0.8-0.9 – average;
  • 1 – minimal losses.

When connecting several devices, make a table for convenience. The calculation is made taking into account the active and reactive components.

Formula for three-phase network

Some private houses equipped with electric heating and electric stoves are supplied with a three-phase 380V line. There are two situations that require calculation in this network:

All loads are single-phase, divided into separate groups. The calculation is performed for each phase separately, similar to a single-phase network.

In addition to single-phase appliances and heaters, there are three-phase electric motors. For these devices, power is converted into current using special formulas:

and the current, respectively:

Information! For rough calculations of the current of a three-phase electric motor, it is possible to use the formula I (A) = 2P (kW).

Table on how to convert Amperes to Watts for calculating circuit breakers:

Current of the Machine, AmpereVoltage
220 volt380 Volt
10.22 kW0.38 kW
20.44 kW1.31 kW
30.66 kW1.97 kW
40.88 kW2.63 kW
51.1 kW3.29 kW
61.32 kW3.94 kW
81.76 kW5.26 kW
102.2 kW6.57 kW
132.86 kW8.55 kW
163.52 kW10.52 kW
204.4 kW13.15 kW
255.5 kW16.44 kW
327.04 kW21.04 kW
408.8 kW26.30 kW
5011 kW32.87 kW
6313.86 kW41.42 kW
8017.6 kW52.59 kW
10022 kW65.74 kW

Calculation of power in a DC network

The easiest way to convert amps to watts is for DC devices. In these devices it is used in its simplest form. In everyday life, such a calculation is most often made when repairing automotive electrical wiring and connecting LED strips.

These strips are connected to the power supply and to select it you need to know the current consumption of the LED devices. If the choice of unit is made incorrectly, it will be overloaded and burn out, or vice versa, the power of the device will be excessive. Such a block is more expensive and has larger dimensions.

On the housing of power supplies designed specifically for LED strips, the output voltage, current and power are indicated, but on some devices the power is not indicated.

In this case, it can be calculated using the formula P=U*I. For a device with an output voltage of 12V and a current of 1.4 A, P=12V*1.4A=16.8 W. Taking into account the 20% power reserve, such a power supply is enough to connect 1 meter of LED5050 strip.

You can do it differently and determine the current consumption of the LEDs. When installing a strip with a power of 14.4 W/m indicated on the tag, the current consumption of 1 meter will be I=P/U=14.4W/12V=1.2A. With a tape length L of 3 meters, the total current I=1.2 A*3m=3.6 A.

An example of converting Amperes to Watts in a single-phase network

Calculation for a single-phase network is most often carried out for household electrical wiring. Cosφ in this case is taken equal to 1, but difficulties arise due to the non-simultaneous inclusion of all electrical appliances.

For example, all kitchen outlets are connected to a 25A circuit breaker. These sockets include a 2kW electric kettle, 1.2kW electric oven, 0.8kW microwave oven, 3.5kW dishwasher and 3.5kW washing machine. Which of these devices can be turned on at the same time?

First of all, you need to find out the total power of the devices that can be connected to the machine. For this, the formula P=U*I=220V*25A=5500V=5.5 kW is used. As can be seen from the calculation, it is allowed to simultaneously turn on a kettle, oven and microwave without a dishwasher and washing machine, or one of these devices and one of the devices of lower power.

Converting Amperes to Watts for a three-phase network

Let's say you have a private house and use a three-phase input to connect it. A three-pole 32 Ampere circuit breaker is installed in the water shield. How much power is this? In order to convert amperes into watts in this case and find out what maximum power can be connected in this case, we will use the above formula (assuming that cos(φ) = 1):

P=380*32*1.73=21036 W ≈ 21 kW

Another example, if there is a three-phase input in the house and a 25A input circuit breaker, the total power of simultaneously switched on electrical appliances will be:


Important! Such power can only be connected if the load is equally distributed across the phases.

The actual load in a residential building consists of a large number of electrical appliances of different power and is unevenly distributed.

Another example of how you can find the current for a three-phase motor when connected with a star:

Formulas for converting amperes to watts and vice versa are necessary primarily at home, but their knowledge will not be superfluous for electricians working in industrial enterprises.

Relationship between power and current in a three-phase network

The principle of calculating power and current for three-phase networks remains the same. The main difference is a slight modernization of the calculation formulas, which allows us to fully take into account the design features of this type of wiring.

The following expression is traditionally taken as a basic relationship:

W =1.73* U*I, (4)

and U in this case represents the linear voltage, i.e. is U = 380 V.

From expression (4) follows the advantage of using three-phase networks in justified cases: with such a wiring diagram, the current load on individual wires drops to the root of three times with a simultaneous threefold increase in the power supplied to the load.

To prove the last fact, it is enough to note that 380/220 = 1.73, and taking into account the first numerical coefficient we get 1.73 * 1.73 = 3.

The above rules for the connection of currents and power for a three-phase network are formulated in the following form:

  • one kW corresponds to 1.5 A of current consumption;
  • one ampere corresponds to a power of 0.66 kW.

Let us point out that everything that has been said is true in relation to the case of connecting the load with a so-called star, which is most often encountered in practice.

A triangle connection is also possible, which changes the calculation rules, but it is quite rare and in this situation it is advisable to contact a specialist.

How to translate

The basic formula reflecting the dependence of electric current indicators on each other is as follows: P = U*I, where U denotes voltage in volts, I is current in amperes, and P is power in watts. Everyone knows the ratio from school physics, which sometimes people forget. Actually, knowing this ratio, you can carry out all further operations yourself, however, there are some subtleties that we will discuss below.

Power Expression

Theoretically, to obtain a particular value, you only need to transform the formula. For example, to find voltage: U=P/I. For example, in Russia, household electrical networks are energized at 220 V. With a power equal to, say, 220 W, the current will be 1 A (220/220). However, this calculation is only valid for a constant voltage network.

If we convert amperes to watts on an alternating voltage network, its actual, effective value should be used. Most often, this is what is indicated as nominal. If only the amplitude value is known, it should be reduced to the effective value by dividing by 1.41 (a rounded number, but sufficient for everyday calculations, the square root of two). And then, using the formula, calculate the power.

Expression of current strength

Often, when choosing a suitable socket, plug, circuit breaker, meter and other similar equipment, it becomes necessary to find the current strength in the network. To do this, the formula is converted to the following form: I=P/U. Considering that power is often indicated in kilowatts, this figure should be converted to watts by multiplying by 1000.

If the voltage is in kilovolts, it cannot always be converted to volts by multiplying. This is due to the fact that this figure is often rounded. For example, the value of 0.4 kV is used in both Russia and Europe, but indicates an actual voltage of 380 V and 400 V, respectively. This means that European loads will remain operational in Russian networks at reduced voltage, but the opposite is not guaranteed.

The essence of the phenomenon

In a DC circuit, 1 VA is the equivalent of one watt (1 W). Power (P) (in watts) in a DC circuit is equal to the product of voltage (V) in volts and current (I) in amperes: P = VI


In an AC circuit, power and V•A mean the same thing when there is no reactance. It is introduced when the circuit contains an inductor or capacitor. Since most AC circuits contain reactance, the V•A value is greater than the actual power dissipated or delivered in watts. This can cause confusion regarding power supply specifications.

For example, the power supply may be rated at 600 V•A. This does not mean that it can output 600 watts if the equipment has no reactance. In real life, the P rating of a power supply is 1/2 to 2/3 of the actual V•A.

Important! When purchasing an uninterruptible power supply for use with electronic equipment, including computers, monitors, and other peripherals, you must ensure that the V•A specifications for the equipment are used in determining the minimum ratings for it. The V•A rating is nominally 1.67 times (167%) more watts.


Unit conversion rules

In the instructions for many devices there are designations in volt-amperes. Their distinction is necessary only for specialists for whom these nuances are important professionally, but for ordinary consumers this is not so important, because the designations used in this case characterize almost the same thing. As for kilowatt/hour and just kilowatt, these are two different quantities that should not be confused under any circumstances.

To determine electrical power through the network current indicator, you can use various tools with which measurements and calculations are made:

  • using a tester;
  • using clamp meters;
  • making calculations on a calculator;
  • using special reference books.

Using a tester, we measure the voltage in the electrical network we are interested in, and then use a current clamp to determine the current strength. Having obtained the necessary indicators and applying the existing formula for calculating direct and alternating current, you can calculate the power. We divide the existing result in watts by 1000 and get the number of kilowatts.

Single phase electrical circuit

Basically, all household electrical networks are single-phase networks that use a voltage of 220 volts. The load marking for them is written in kilowatts, and the current strength is in amperes and is designated as AB.

To convert one unit to another, the formula of Ohm's law is used, which states that power (P) is equal to current (I) multiplied by voltage (U). That is, the calculation will look like this:

W = 1A x 1V

In practice, such a calculation can be applied, for example, to the designations on old electricity meters, where the installed machine is designed for 12 A. Substituting digital values ​​into the existing formula, we get:

12A x 220V = 2640 W = 2.6 kW

Calculations for an electrical network with direct and alternating current are practically no different, but are valid only in the presence of active devices that consume energy, for example, incandescent electric lamps. And when devices with a capacitive load are connected to the network, then a phase shift appears between current and voltage, which is the power factor, written as cos φ. When there is only an active load, this parameter is usually equal to 1, but when there is a reactive load in the network, it must be taken into account.

In cases where the network load is mixed, the value of this parameter fluctuates around 0.85. Reducing the reactive component of power leads to a reduction in losses in the network, which increases the power factor. Many manufacturers, when marking a device, indicate this parameter on the label.

Three-phase electrical network

If we take the example of a three-phase network, then everything is somewhat different here, since three phases are involved. When making calculations, you need to take the value of the electric current of one of the phases, which is multiplied by the voltage in this phase, after which the resulting result is multiplied by cos φ, that is, by the phase shift.

Having thus counted the voltage in each phase, we add up the results and obtain the total power of the device, which is connected to a three-phase network. In formulas it looks like this:

Watt = √3 Ampere x Volt or P = √3 x U x I

Ampere = √3 Volt or I = P/√3 x U

It must be borne in mind that there is a difference between phase and line voltage and current. But the calculation formula remains the same, except for the case when the connection is made in the form of a triangle, and it is necessary to calculate the load of an individual connection.

For circuits with alternating current, there is an unspoken rule for this calculation: the current strength is divided in half to select the power of the protective and starting relays. The same rule applies when calculating the diameter of the conductor in such electrical circuits.

Why is there a need to move from amperes to kilowatts and back?

It is impossible to reduce the description of an electrical network to just one unit. The need to use two different units of measurement of parameters arises due to the fact that in the vast majority of cases, a particular wiring serves several consumers, each of which contributes to the strength of the flowing current.

As a result

  • It is convenient to calculate the cross-section of the wires based on the maximum strength of the current flowing through them;
  • circuit breakers that protect receivers and wires from overload and short circuit are selected in the same way;
  • The main characteristic of any electrical device connected to a socket as a current collector or load is traditionally its power.

The popularity of indicating power consumption, as one of the main parameters of an electrical appliance, is also determined by the fact that payment for electricity is carried out using an electric meter, which is calibrated in kWh.

Accordingly, given the known cost of one kW*hour, payment for electricity is determined by simply multiplying three numbers: power, operating time and cost of one kW*hour.

Taking into account the peculiarities of determining electricity costs, it becomes clear the advantage of using for powerful devices not useful power, measured in kW, but total power, which is determined in kVA.

It is advantageous in that it makes it possible to perform calculations using a single method without separately taking into account the actual phase shift of current and voltage.

The principle of identical calculations when knowing the total power also applies to current calculations.

The conversion from one unit to another is carried out according to the relations (1) and (2) presented above and, due to their simplicity, does not pose any big problems.

In this case, the fact that voltage U can be considered a constant, which varies only depending on the number of wiring phases, plays a role.

Below we present the basic rules for performing such calculations in relation to the most common cases in practice.

Conversions from amps to kilowatts and vice versa

You can convert values ​​in three ways: a universal table, an online calculator or a formula. As for using the calculator, you need to insert the initial indicators into the appropriate fields and press the button. It is convenient to use this system when you have to deal with large digital values.

Note! According to the universal table and formula, you can find out that one A contains 0.22 kW or 0.38 kW. You can convert values ​​using the available numbers using a calculator or by multiplying by the given value. For example, to calculate how much 6A will be in kW, you need to multiply 0.6 by 0.22. The result will be 1.32 kW.

In a single-phase electrical circuit

To calculate the required values ​​in a single-phase network, where the rated current of the circuit breaker, for example, is 10 A and in normal condition no energy flows through it above the specified value, it is necessary to calculate the maximum electrical power. You need to substitute the values ​​of voltage and electric current into the formula for finding power and multiply them together. It turns out that the power will be equal to 220*10=2200 watts. To convert to smaller values, you need to divide the figure by 1000. The result is 5.5 kW. This is the entire amount of power supplied from the machine.

Translation in a single-phase electrical circuit

In a three-phase electrical circuit

The conversion of indicators in a three-phase network designed for 380 volts can be done in a similar way. The difference lies in the formula. To determine the required data, you need to substitute the root of three into the product of voltage and electric current. For example, the machine is designed for 40 A. By substituting the values, you can get 26327 W. After dividing the value by 1000, the result is 26.3 kW. That is, it turns out that the machine will be able to withstand the load.

With a known power indicator of a three-phase circuit, the operating current can be calculated by transforming this formula. That is, the electrical power must be divided by the root of 3 multiplied by the voltage. As a result, if the electrical power is 10 kW, the value of the machine will be 16A.

Translation in a three-phase electrical circuit

Relationship between basic quantities

The most common task faced by ordinary consumers is calculating the actual current strength. So how to correctly calculate amperage based on known voltage and power values? It is necessary to solve it by justifying the cross-sectional values ​​of the cores and the rating of the machine, having technical information about the devices that will be powered into this circuit.

After calculating the current, cables with the smallest permissible cross-section are often selected. However, this is not always correct, since such a solution leads to significant restrictions when it is necessary to add new electrical appliances to the network.

Sometimes it is necessary to carry out reverse calculations and determine what total power can be connected to devices at a known voltage and maximum permissible current, which is limited by existing wiring.

You can solve these two problems for a single-phase circuit using a simple formula:

I = S/U;

S = U * I,

where S is the total total power of all electrical consumers.

A pie chart reflecting Ohm's law and expressing the dependence of power, current, voltage and resistance is suitable for calculating the parameters of a single-phase circuit

To solve the problem of calculating current using known or calculated values ​​of power and voltage in a three-phase circuit, you need to know the total load imposed on each phase.

Both the required cross-section of the cable cores and the minimum permissible rating of the machine are selected according to the busiest line, considering that:

S = 3 * max{S1, S2, S3}.

I = S / (U * 1.73).

The permissible power for each phase can be calculated using the following formula:

S1,2,3 < S / 3 = I * U / 1.73,

where I is the maximum permissible current for existing wiring.

Necessary calculations

First you need to check the sockets that are connected to the selected machine. Sometimes an automatic device powers not only household appliances, but also lighting devices. If the electrical wiring in the house is not installed correctly, the entire supply may depend on only one device. They count the total number of consumers and add up the voltage they need to operate.

The result will be the sum of watts that the automatic device supplies to these devices. Most likely, the equipment will not be connected at the same time, but the formula will make it possible to calculate the maximum voltage consumption. If some device does not indicate a specific power, but its interval, then it is necessary to take the largest value.

Minimum values ​​are not taken into account, since in this case the machine will operate at full load. This is unacceptable, because there are interruptions in the network, and this will lead to breakdown of the disconnecting device. The voltage in private homes and in industrial enterprises is different. There are two types:

  • single-phase network - 220 V;
  • two-phase - 380 volts.

Convert Volt Amperes to Watts, VA to kW

For calculation use the formula:

Pп (apparent power, kVA) = Pa (active power, kW)*cos ϕ.


  • generator power in normal operating mode – 8 kW;
  • The documentation for the connected machine indicates the power consumption:

7 kW and cos ϕ = 0.8

  • When connecting such a load, the power source will not be able to provide the required operating mode:

8*0.8=6.4 kW.

Single-phase network

In private homes, the voltage does not exceed 220 volts. In this case, you need to make calculations specifically for a single-phase network. General physical formula for voltage: U = P/I, where:

  • U is voltage;
  • P - electrical power;
  • I is the current strength.

The result makes it possible to measure consumption in watts, but usually a value such as kilowatt is used. To do this, you need to divide the resulting number by 1000 (1 kW = 1000 W). You can understand the algorithm for calculating how many amperes are in 1 kilowatt using an example.

If in a single-phase network the consumption is 220 V, then the rating of the automatic device is calculated as follows: 220/200 = 1 ampere. If all devices use a total power of 0.13 kW, then you will need an automatic machine with 6 amperes (0.13/220 = 6 A). That is, now you can find out how many amperes are contained in kW: 1000/220 = 4.5 A.

Reverse calculations can be done in a similar way. If the network has a 5 A disconnect device, then you can determine the maximum power it can handle. In this case, amperes are multiplied by volts: 5x220 = 115 W. If the devices consume more power, then the machine will not be able to withstand it, it must be replaced with another. You can use the table for converting amperes to watts and kilowatts:

  • 2 A = 0.4 and 1.3 kW for single- and three-phase networks, respectively;
  • 6 amperes are 1.3 and 3.9 kilowatts;
  • 10 A = 2.2 and 6.6 kW;
  • 16 A - 3.5 kW for single-phase and 10.5 for a network with a voltage of 380 V;
  • 20 amperes = 4.4 and 13.2 kilowatts;
  • 25 A - 5.5 and 16.4 kW.

Determination of power by current strength for a single-phase network

The need to perform this procedure most often arises when setting restrictions on the maximum power of an electrical appliance that can be connected to a specific outlet or group of outlets.

If this restriction is violated, the risk of fire increases, and the plastic decorative elements of the outlet may melt due to excess heat generated.

Based on the definitions, which are described in mathematical form by expressions (1) and (2), to find the power, you simply multiply the current by the voltage.

The maximum permissible current is indicated on the outlet marking and for most indoor household products of this type is usually 6 A.

The voltage supplied from the mains to the outlet is 220 - 230 V. Thus, the maximum power is 1.3 kW.

Separately, we point out that the risks of damage to the outlet when connecting an overly powerful device are minimal in properly designed household wiring.

This useful property is provided by:

  • installation of automatic machines;
  • the use of plugs in powerful electrical appliances that physically cannot be connected to conventional sockets (mechanical interlocking).

A rather popular direct connection of a powerful stationary device (air conditioner, boiler) to the network without the use of sockets can be considered a unique version of mechanical interlocking.

Voltage 380 volts

Calculations for a three-phase network are carried out using a different formula. The voltage in such rooms is 380 V, it is distributed over three wires. Therefore, it is possible to install an automatic shutdown device with a lower rating at the same power consumption. The formula looks like this: P = U x I x root of 3. This way you can find out how many watts are in 1 ampere. To determine the number of kW, you need W x (0.7 x 380).

You can better understand the peculiarities of the calculations using an example. The three-phase network voltage is 380 V, and power supply devices require 0.13 kW of power. You need to find out which machine is best to buy for such a room. To do this, use the formula: 130/380 = 0.5 amperes.

In a similar way, calculations can be carried out for a two-phase network. Its voltage is 266 V. One kilowatt will contain 3.7 A (1000/266). Accordingly, one ampere is equal to 266 watts. For a room with a two-phase network and a power consumption of 250 watts, a machine with a rating of 3.7 amperes is suitable. When choosing a device, you need to take into account the current strength, which is less in a three-phase network for the same amount of power consumption.

What is "watt"

Halogen - chemical and physical properties of gas

This measurement unit belongs to the international classification SI and is a derivative. It is described as a power indicator at which 1 joule of energy is expended per second. It can also be given the following characteristic: it describes how quickly work is performed to maintain a constant speed of an object of 1 meter per second, forced to overcome the action of a force of 1 Newton, the vector of which is opposite to that of the moving body. To describe electromagnetic phenomena, the representation of a watt is also used as the rate of transformation of electricity with an electric current of 1 A flowing through a circuit fragment with a potential difference of 1 volt. An LED light bulb typically has a power consumption of several watts. Based on this, it should be clear that questions like “how many watts are in a volt” are irrelevant - these units describe completely different physical quantities.

In writing, the unit is usually denoted as “W” or “W”. The name itself was given by the name of the Scottish mechanic James Watt, who invented the steam engine. The unit was adopted for use in measuring power in 1882, and entered the SI system in 1960. Previously, the same quantities were usually measured in horsepower. A measuring device – a wattmeter – will help you find out the power parameters. For electrical appliances for professional or household use, the power consumption is indicated in the technical documentation attached to them, for example, in the device passport. On thyristors and other electronic components, the value is sometimes indicated by markings on the case.

James Watt

It is generally accepted that the total power value in practice, characterizing the actual load level introduced by the consumer to the components connected to the electrical network (switchboards, cable elements, transformer and other devices), is determined by the current consumption. Therefore, for transforming and switching devices, the power rating is described in the watt form, and not in the volt-ampere form.

Efficiency is also called power factor or cos fi. It is a dimensionless quantity that changes the current in accordance with the reactive component in the load. The coefficient illustrates the amount of alternating current passing through a phase shift relative to the applied voltage. The name cos fi denotes the cosine of a given phase shift.

An example is a hammer drill, the instructions for which indicate a consumption figure of 5 kW and a coefficient of 0.85. Then the full indicator required for its operation (in volt-amperes) will be equal to the quotient of these values: 5/0.85 = 5.89 kVA.

An electric kettle is an example of a device that does not have reactive power

Terms of transfer

Calculation formulas will be useful both when purchasing a new circuit breaker and when choosing household appliances.

It is necessary to convert one value into another when choosing a cable cross-section for power. To do this, you need to find out the total current required by home appliances, taking into account their power. In some cases, reverse calculations are performed.

The ability to do physical calculations will not become unnecessary information; sometimes this knowledge can come in handy. Voltage in any network can become dangerous, so electrical wiring must be handled with care and attention. Incorrect connection leads to burnt wires or overloads of the automatic device. Formulas allow you to find out how many volts, watts and kilowatts are in 1 ampere.

Reasons for making a transfer

Power and current are key characteristics necessary for the proper selection of protective devices for equipment powered by electricity. Protection is needed to prevent melting of the wiring insulation and breakdown of units.

Electrical wiring supplying lighting, an electric stove, and a coffee machine must be protected by individually selected devices. After all, each consumer creates “its own” load - in other words, consumes a certain current.

By the way, the cables and wires that supply the listed household devices have a certain current-carrying capacity. The latter is dictated by the cross-section of the cores.

Each protective device must operate at the moment of a voltage surge that is dangerous for the type of equipment being protected or a group of technical devices. This means that RCDs and machines should be selected so that during a threat to a low-power device, the network is not completely disconnected, but only the branch for which this surge is critical.

The housings of the circuit breakers offered by the retail chain are marked with a number indicating the maximum permissible current. Naturally, it is indicated in Amperes.

But on the electrical appliances that are required to protect these machines, the power they consume is indicated. This is where the need for translation arises. Despite the fact that the units we are examining belong to different current characteristics, the connection between them is direct and quite close.

Amperes and kilowatts, which characterize the power consumption of household devices, help you choose the right protection.

Voltage is the potential difference, in other words, the work put into moving a charge from one point to another. It is expressed in Volts. Potential is the energy at each point where the charge is/was.

Current strength refers to the number of Amperes passing through a conductor in a specific unit of time. The essence of power is to reflect the speed at which the charge moved.

Power is indicated in Watts and Kilowatts. It is clear that the second option is used when an overly impressive four- or five-digit figure needs to be reduced for ease of perception. To do this, its value is simply divided by a thousand, and the remainder is rounded up as usual.

Powering high-power equipment requires a higher rate of energy flow. The maximum permissible voltage for it is higher than for low-power equipment. The machines selected for it should have a higher operating limit. Therefore, accurate selection according to the load with competent conversion of units is simply necessary.


How many Watts are in Ampere?

If we are talking about a car network, then in one ampere there are 12 watts at a voltage of 12V. In a household electrical network of 220 Volts, a current of 1 ampere will be equal to the consumer power of 220 Watts, but if we are talking about an industrial network of 380 Volts, then 657 Watts per ampere.

12 amps how many watts?

How many watts of power at 12 amperes of current consumption will depend on the network voltage with which the consumer himself operates. So 12A it could be: 144 Watts in a 12V car network; 2640 Watts in a 220V network; 7889 Watts on a 380 Volt power supply.

220 watts how many amps?

The current strength of a 220 Watt consumer will differ depending on the network in which it operates. This can be: 18A at a voltage of 12 Volts, 1A if the voltage is 220 Volts, or 6A when current consumption occurs in a 380 Volt network.

5 amps how many watts?

To find out how many watts a 5 ampere source consumes, just use the formula P = I * U. That is, if the consumer is connected to a car network where there is only 12 Volts, then 5A will be 60W. When consuming 5 amperes in a 220V network, it means that the consumer’s power is 1100W. When the consumption of five amperes occurs in a two-phase 380V network, the source power is 3290 Watts.

Why do you need to convert amperes to kilowatts?

People have long been accustomed to the fact that on their electrical appliances the amount of energy consumed is indicated in kilowatts. But fuses, plugs and automatic sockets are marked in amperes, and not everyone will understand the first time how many kilowatts we are talking about. When faced with such a problematic situation, people wonder how to convert one value to another, what scheme to use for this, and what will it yield.

It is precisely because users have problems with these two concepts that electrical accessories and protective equipment are often selected incorrectly, which is extremely harmful. That is why every owner of a private house or apartment needs to learn how to independently deal with such values ​​so that the electricity system functions correctly and safely.



Object of measurement

To determine volt-amperes (V•A), you will need to perform the following measurements:

  1. First you will need to measure the current in amperes (A). This is the SI unit of I.
  2. Next, the voltage should be measured in SI units - volts. It will show the force required for the flow of electric current in volts (V).
  3. Calculate P - the amount of energy produced by current and volts together. Multiplying amperes (A) by volts (V) gives the resultant or energy.

You may be interested in: Features of current resonance

Measuring quantities

Direct current (—), or DC, is inherent in the process when it flows in one direction, for example, a flashlight with a battery uses a constant indicator. Alternating current (~) or AC refers to processes with alternating direction of electron movement, due to which it periodically changes its direction. In North America and Western Japan this occurs 60 times per second at a frequency of 60 Hz. In Russia, the EU, most of Australia, South America, Africa and Asia, the frequency is 50 Hz.

Watt's law formula

To convert these quantities, the formula of Watt's law is used:

Power (P) = Current (I) x Voltage (V), the same in units: watt = ampere x volt. To find amplifiers, use the Watt formula in reverse and divide the power by the voltage: Current (I) = Power (P) ÷ Voltage (V) I = 600 W : 120 V, then the value of I = 5A

Note! When specialists operate with large dimensions P, they use kilowatts (kW), 1 kW = 1000 W.

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