Watts to Amps Calculator

Converting Watts to Amps

Knowing how many amps a device draws from a given power rating helps with wire sizing, fuse selection, and circuit planning. This calculator is the inverse of the amps-to-watts formula and supports DC, single-phase AC, and three-phase AC.

Formulas

DC:

$$I = \frac{P}{V}$$

AC single-phase:

$$I = \frac{P}{PF \times V}$$

AC three-phase (line-to-line):

$$I = \frac{P}{\sqrt{3} \times PF \times V_{L-L}}$$

AC three-phase (line-to-neutral):

$$I = \frac{P}{3 \times PF \times V_{L-N}}$$

Practical Notes

A 1200 W heater on a 120 V single-phase circuit with PF = 1 draws 10 A. For three-phase motors, use the nameplate voltage and power factor. Related tools: Amps to Watts Calculator and Wattage to Amperage Calculator.

Frequently Asked Questions

How is this different from wattage to amperage?

Both use the same physics (P = V × I). This tool mirrors the amps-to-watts calculator layout with detailed step-by-step output and three-phase voltage type options.

What power factor should I use?

Resistive loads (heaters, incandescent bulbs) have PF ≈ 1. Motors and fluorescent lights often run 0.8–0.95. Check the device nameplate when available.

Why is three-phase current lower?

Three-phase power is distributed across three conductors. For the same total power, each phase carries less current than a single-phase circuit at the same voltage.

Can I convert amps back to watts?

Yes. Use the Amps to Watts Calculator, which applies the forward power formulas for the same circuit types.

Does this account for motor efficiency?

This calculator uses input power (watts drawn from the supply). Motor output horsepower requires an additional efficiency conversion.

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Watts to Amps Calculator

Converting Watts to Amps

Formulas

Practical Notes

Frequently Asked Questions

Related Tools

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