watts to amps

The number on a breaker is amps, but the number on every appliance is watts — so the entire electrical trade converts watts to amps at the circuit voltage: I = P/V. A 1,800 W heater on 120 V draws exactly 15 A, which is why a 15 A breaker is the standard US branch circuit. This calculator is the load-calculation workhorse.

By EnginStack Editorial Team | Reviewed against NIST, BIPM and primary-source documentation About →
watts
volts
— amps
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Constants verified against NIST Special Publication 811 (Guide for the Use of the International System of Units) and the 1959 International Yard and Pound Agreement. All values are exact — none are rounded approximations.

watts to amps

Every National Electrical Code load calculation works this way: sum the connected watts, divide by the circuit voltage, and the result tells you the breaker and wire size. At 120 V, 1,800 W is 15 A; at 240 V the same watts need only 7.5 A — which is why high-power appliances run on 240 V. The 80% rule (a continuous load should not exceed 80% of breaker rating) makes this conversion the first step of every circuit design.

amps = watts ÷ volts
I = P/V
Exact watt's law — the ratio of the power and voltage you provide.

Common watts to amps Values

wattsvoltsampsContext
1,800 W120 V15 AFull load on a 15 A breaker.
1,440 W120 V12 A80% rule continuous load.
3,600 W240 V15 ADryer on a 240 V circuit.
600 W120 V5 AMicrowave.
120 W12 V10 AAutomotive accessory.

Engineering Context

Watts-to-amps is the most-used electric conversion on this site — it is the inverse of amps to watts, and the breaker-size step in every circuit design. The watts input connects to the energy hub's watts to kW, and the wire-size output connects to AWG to mm². The electric hub collects the full family.

More: A to W · V to A · AWG to mm² · Electric Hub

Related Unit Converters

Amps To Watts Volts To Amps Awg To Mm2 Electric Converters

Frequently Asked Questions

How do I convert watts to amps?

Divide watts by volts: I = P/V. A 1,800 W heater on 120 V draws 15 A. At 240 V, the same heater draws only 7.5 A.

What is the 80% rule for breakers?

The NEC says a continuous load (running 3+ hours) should not exceed 80% of the breaker rating. So a 15 A breaker handles 12 A continuous = 1,440 W at 120 V. This converter shows both the raw and the derated amps.

How many watts can a 15-amp circuit handle?

At 120 V, 1,800 W at full rating, or 1,440 W continuous per the 80% rule. Multiply the breaker amps by the circuit voltage and you have the watts — the exact inverse of this calculator.