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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.

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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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