Watts to Amps Calculator
Enter the power in watts and the voltage. Pick the circuit type to get the current in amps, and see a 125 percent figure for sizing a circuit for a continuous load.
How to use this Watts to Amps Calculator
- Enter the power of the load in watts.
- Enter the voltage of the supply, such as 120, 240 or 208.
- Choose DC, single-phase AC or three-phase AC.
- For AC, enter the power factor. Use 1 if you do not know and the load is a heater.
- Press Calculate to see the current and the 125 percent figure.
How to convert watts to amps
The formula depends on the type of circuit.
- DC: amps = watts / volts
- Single-phase AC: amps = watts / (volts x power factor)
- Three-phase AC: amps = watts / (1.732 x line voltage x power factor)
- Continuous load: amps x 1.25
Worked example
A 1,500 W heater on a 120 V single-phase circuit with a power factor of 1 draws 1,500 / 120 = 12.50 A. At 125% for a continuous load that is 15.63 A, so the next standard breaker size is 20 A. For a three-phase motor of 10,000 W on 208 V with a power factor of 0.9, the current is 10,000 / (1.732 x 208 x 0.9) = 30.84 A.
A circuit should never run at its limit for hours. Many rules size the breaker and the wire for 125% of a continuous load, and then round up to a standard size. Power factor matters for motors and other inductive loads. At a low power factor the same watts need more current, so the wire and breaker need to be larger. Use the wire size calculator to check the wire for this current.
Assumptions & limits
- The standard breaker sizes list is a simplified set of common sizes. Not every size applies to every circuit. Check the National Electrical Code and your local rules, and use a licensed electrician for real installations.
- The 125 percent figure applies to continuous loads in many rules. Motors, heaters and other loads can have their own rules.
- The three-phase formula uses line to line voltage and a balanced load.
- Power factor is an input. Use the figure from the label or data sheet.
- The calculator converts values. It does not check whether a circuit is safe.
Frequently asked questions
How do I convert watts to amps?
Divide the watts by the volts for DC. For AC also divide by the power factor, and for three-phase use 1.732 times the line voltage.
How many amps is 1500 watts at 120 volts?
12.5 amps with a power factor of 1.
What is power factor?
It is the ratio of real power to apparent power in an AC circuit. Resistive loads have a power factor of 1.
What is a continuous load?
A load that runs for three hours or more. Many rules size the circuit current at 125 percent for it.
How do I find the breaker size?
Take 125 percent of a continuous load current and round up to a standard breaker size, then check the wire and the code.
Can I convert amps to watts too?
Yes. Multiply the amps by the volts, and by the power factor for AC.
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Last updated: November 2026