Calculators / Power and wiring

Watts to amps

Put in the watts off the label and the voltage. You'll get the amps, and whether it fits a regular circuit or needs its own.

Updated November 2026 · How we check our numbers

Converted

1,500 W = 12.5 amps

At 120 V. That runs on a regular 20 A circuit, counted at 125% since it runs for hours, as long as nothing else big shares it.

Amps: 12.5 A
Watts: 1,500 W1.5 kW
Breaker: 20 A12.5 A × 1.25 = 15.6 A

Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

What size wire for this circuit12.5 A at 120 V, continuous

amps = 1,500 W ÷ 120 V = 12.5 A

continuous: 12.5 A × 1.25 = 15.6 A → 20 A breaker

Breaker sizes

120 V

15 A breakercarries 12 A for hours at a time
0.5 A short
20 A breakercarries 16 A for hours at a time
Smallest that works
25 A breakercarries 20 A for hours at a time
Bigger than needed
30 A breakercarries 24 A for hours at a time
Bigger than needed
35 A breakercarries 28 A for hours at a time
Bigger than needed
40 A breakercarries 32 A for hours at a time
Bigger than needed
45 A breakercarries 36 A for hours at a time
Bigger than needed
50 A breakercarries 40 A for hours at a time
Bigger than needed
60 A breakercarries 48 A for hours at a time
Bigger than needed

Standard sizes from NEC 240.6(A).

Motors

Compressors, pumps and AC draw more amps than watts ÷ volts, and more again for a second when they start. For those, use the amps on the nameplate.

At 240 V

The same 1,500 W at 240 V is 6.3 A. Doubling the voltage halves the amps, which is why big loads run on 240 V.

How we work it out

On a house circuit, amps are watts divided by volts.

amps = watts ÷ volts

That's exact for heaters, kettles, ovens and anything else that just makes heat. Motors, like compressors, pumps and AC, draw more than that, so use the amps on their nameplate instead.

Then the breaker: the next standard size at or over the load. If it runs 3 hours or more at a time, the NEC sizes it at 125% (210.19 and 210.20). A 1,500 W space heater is 12.5 A, so 15.6 A as a continuous load, which takes a 20 A circuit.

Where the numbers come from

NFPA 70 (NEC), free access edition

Guides

Wire gauge chart (printable)

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