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Enter the current and the voltage, choose DC, single-phase or three-phase AC, and add the power factor for motors and power supplies. The result shows watts, kilowatts and kVA. Switch the direction to get amps from watts.

Enter your values

Pick what you know and what you want to find.
Household sockets are single-phase AC.
Where do I find this?

Batteries, solar panels, car and USB circuits are DC. Normal wall sockets are single-phase AC.

Three-phase is used for electric stoves, wallboxes, workshops and large motors.

120 V in North America, 230 V in most of Europe, 12 or 24 V for DC systems.
Where do I find this?

The voltage is on the device's label. For three-phase use the voltage between two phases, for example 400 V or 208 V.

From the label or a clamp meter, in amps (A).
Where do I find this?

The label shows the rated current in A. A breaker or fuse rating is the maximum the circuit allows, not what the device draws.

Between 0.1 and 1. Use 1 for heaters and kettles, about 0.8 to 0.9 for motors if unknown.
Where do I find this?

Pure heating loads have a power factor of 1. Motors, compressors and many power supplies are lower; 0.8 to 0.9 is a common estimate.

Result

Enter your values to see the result.

Power
– W
Power
– kW
Apparent power
– kVA

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How it is calculated

  • DC: watts = volts × amps
  • AC single-phase: watts = volts × amps × power factor
  • AC three-phase: watts = √3 × volts × amps × power factor (volts between two phases)

Example

A device drawing 10 A on a 120 V outlet with power factor 1 uses 120 × 10 = 1,200 W, or 1.2 kW. On 230 V the same 10 A is 2,300 W.

What this estimate leaves out

Real devices vary with load and temperature, and motors draw several times their running current when they start. Use this for planning; ask a qualified electrician before you size cables, breakers or fuses.

Written and reviewed by QLines, Cologne · Last reviewed

FAQ

Frequently Asked Questions

How do you convert amps to watts?

Multiply the amps by the volts: watts = amps × volts. For AC devices with motors also multiply by the power factor, and by √3 (about 1.73) for three-phase.

How many watts is 10 amps?

At 120 V, 10 A is 1,200 W. At 230 V it is 2,300 W. At 12 V DC it is 120 W.

How do I convert volts to watts?

You also need the current: watts = volts × amps. Volts alone do not tell you the power.

How many watts can a 15 A circuit carry?

A 15 A circuit at 120 V can carry 1,800 W at most; for continuous loads electricians usually plan with 80 %, about 1,440 W.

More free calculators

Watts to Amps Calculator

Convert watts to amps or amps to watts for DC, single-phase and three-phase circuits.

kVA to Amps Calculator

Convert kVA to amps, or amps to kVA, for single-phase and three-phase supplies, generators and transformers.

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