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Watts to Amps Calculator (DC, AC, 3-Phase)

This watts to amps calculator converts watts to current for DC, single-phase AC, and three-phase circuits using volts and power factor.

Circuit

Three-phase uses line-to-line volts. Power factor applies to AC only and starts at 1.0 for a resistive load.

Real power of the load, in watts.

Supply voltage. Household circuits are often 120 V or 240 V.

Household examples

Each example switches to single-phase AC with a power factor of 1.

Current

10 A

DC current

I = P / V = 1,200 / 120 = 10 A

At 120 V, 15 A is 1,800 W. Continuous loads are often kept to about 80% of that, or 1,440 W.

This current is a starting point. Breaker and wire sizing follows the electrical code; ask a licensed electrician.

How to use

  1. Choose DC, single-phase AC, or three-phase (line-to-line).
  2. Enter watts and volts. For three-phase, volts are line-to-line.
  3. For AC, enter the power factor. Use 1.0 for a resistive load such as a heater. DC does not use power factor.
  4. Read the current in amps, or use a 120 V or 240 V household example. Clear empties the fields.

Formula

DC current is I = P / V. Single-phase AC is I = P / (PF × V). Three-phase line-to-line current is I = P / (√3 × PF × Vll), where √3 is about 1.732. Power factor is greater than 0 and at most 1, and it is not used for DC. Volts must be greater than 0.

Example. A 1,200 W load on 120 V DC draws 1,200 / 120 = 10 A. On single-phase AC with a power factor of 0.8, the same load draws 1,200 / (0.8 × 120) = 12.5 A.

Example. 10,000 W on a 208 V three-phase circuit at power factor 1 draws 10,000 / (√3 × 208) ≈ 27.757 A.

Example. 15 A × 120 V = 1,800 W. The usual 80% continuous-load rule is about 1,440 W. This page does not size a breaker or a wire.

Breaker and wire sizing

The amps here are the current a load draws at the volts and power factor you enter. They are not a breaker size or a wire size. Continuous loads are often limited to 80% of the breaker rating, and conductor size also depends on the electrical code, temperature, and how the wire is installed. Ask a licensed electrician before you choose a breaker or conductor.

Frequently asked questions

How do I convert watts to amps?

For DC, amps = watts / volts. A 1,200 W load on 120 V draws 10 A.

What about AC circuits?

Single-phase AC: amps = watts / (power factor × volts). Three-phase: amps = watts / (1.732 × power factor × line-to-line volts).

How many watts can a 15 amp circuit handle?

15 A × 120 V = 1,800 W. For continuous loads, the usual 80% rule limits you to about 1,440 W.

What is power factor?

The ratio of real power to apparent power. Resistive loads like heaters are close to 1.0; motors are often lower.

Can I use this to size a breaker or wire?

Use it as a starting point only. Breaker and conductor sizing follows the electrical code; ask a licensed electrician.

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