Watts to Amps Calculator

Convert between watts and amps for any appliance or circuit. Choose the voltage, enter watts or amps, and see the current, the power and the circuit size for a continuous load.

Watts → amps
W
Options
1 for heaters, kettles and light bulbs; about 0.8–0.95 for motors.
Current12.5 A
In kilowatts
1.5 kW
Circuit for a continuous load
20 A or larger (80% rule)

What you will need

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How this calculator works

For single-phase power, amps = watts ÷ (volts × power factor), and watts = volts × amps × power factor. Resistive loads such as heaters and incandescent bulbs have a power factor of 1; motors are lower.

Circuits that carry a load for 3 hours or more should be loaded to no more than 80% of the breaker rating, a rule from the National Electrical Code. The calculator suggests the smallest standard breaker that meets it.

This is a planning tool. Wire size, breaker type and local code requirements must be confirmed by a licensed electrician.

Example: a 1,500 W heater on a 120 V outlet

  1. Amps = 1,500 ÷ 120 = 12.5 A.
  2. 12.5 A is under 80% of a 20 A circuit (16 A), so a 20 A circuit suits continuous use.

Quick reference

Maximum continuous load by circuit (80% rule)
CircuitMax continuous ampsWatts at 120 VWatts at 240 V
15 A12 A1,440 W2,880 W
20 A16 A1,920 W3,840 W
30 A24 A2,880 W5,760 W
40 A32 A3,840 W7,680 W
50 A40 A4,800 W9,600 W

Tips before you buy

  • Two 1,500 W appliances on the same 15 A kitchen circuit will usually trip the breaker.
  • A Level 2 EV charger drawing 32 A needs a 40 A circuit; one drawing 48 A needs a 60 A circuit.
  • Use the generator size calculator to add up running and starting watts before buying a generator.

Common sizes

Guides

Frequently asked questions

How many amps is 1,500 watts?

At 120 V, 1,500 W draws 12.5 amps. At 240 V it draws 6.25 amps.

How many watts can a 15 amp circuit handle?

A 15 A, 120 V circuit can supply 1,800 W, but for continuous loads you should stay under 80%, or 1,440 W.

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Last updated October 26, 2026