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Watts to Amps Calculator

A watts-to-amps calculator converts between power (watts) and current (amps) at a given voltage — both directions — for DC, AC single-phase and AC three-phase, with a power factor for motors and other reactive loads. It's the everyday tool for sizing wiring, breakers and generators.

Your measurements

Result

Voltage and the type of system matter: the same wattage draws very different amps at 120 V vs 240 V, and three-phase brings in a √3 factor. Set those and it gets the current right.

How it is calculated

DC/resistive: A = W ÷ V. AC single-phase: A = W ÷ (V × PF). AC three-phase: A = W ÷ (√3 × V × PF), using line-to-line voltage. Power factor is ~1 for purely resistive loads (heaters, incandescent) and roughly 0.8 for motors. kVA is the apparent power used to size transformers and generators.

Steps

Choose the direction — watts to amps, or amps to watts.
Enter the known value (watts or amps).
Enter the voltage of the circuit.
Pick DC, single-phase or three-phase, and a power factor for AC.
Read the result and the apparent power (kVA) for sizing.

Worked example

1,200 W at 120 V on a resistive circuit draws 10 A (A = W ÷ V).

Common questions

How do I convert watts to amps?

Divide watts by volts for DC or resistive loads (A = W ÷ V). For AC, divide by volts × power factor; three-phase adds a √3 factor.

Why does voltage change the amps?

Power = volts × amps, so for a fixed wattage, higher voltage means lower current. That's why 240 V circuits draw half the amps of 120 V for the same load.

What power factor should I use?

About 1.0 for heaters and incandescent lighting; around 0.8 for motors and many appliances. Check the nameplate.

What's kVA versus kW?

kW is real power (work done); kVA is apparent power (volts × amps). Generators and transformers are rated in kVA, so the calculator shows it.