Question 1

How do you convert watts to amps?

Accepted Answer

For a DC or single-phase circuit, amps = watts ÷ volts (divide by power factor too for AC motors and other reactive loads). For three-phase, amps = watts ÷ (1.732 × line voltage × power factor). Example: 1,500 watts at 120 volts single-phase = 12.5 amps.

Question 2

What power factor should I use?

Accepted Answer

Use 1.0 for purely resistive loads: heaters, incandescent lighting, EV charging. Motors, compressors, and many electronics run lower, often 0.8–0.95; check the nameplate. A lower power factor means more current for the same watts, so it raises the amps.

Question 3

Why does this calculator also show a wire and breaker size?

Accepted Answer

Because the amps only matter once you size the circuit for them. We apply NEC Table 310.16 (75°C copper) and the standard breaker sizes from 240.6, including the 125% rule for continuous loads, so you see the breaker and minimum wire, not just the current. Always confirm with a licensed electrician and your local authority having jurisdiction (AHJ).

Question 4

Is 120V or 240V right for my circuit?

Accepted Answer

Most US household receptacle circuits are 120V. Large appliances (ranges, dryers, water heaters, EV chargers) use 240V. Use the actual circuit voltage; the same wattage draws half the amps at 240V that it does at 120V.

Question 5

How do you convert amps to watts?

Accepted Answer

Multiply amps by volts, and by the power factor on AC. Single-phase: W = A × V × PF. Three-phase: W = 1.732 × A × V × PF. Example: 15 A on a 120 V resistive circuit is 1,800 W. Flip the direction switch above to run it that way.

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