Watts to Amps Calculator
Convert watts to amps using your voltage and power factor, for DC or single-phase AC circuits.
What your result means
Amps is the current the load draws, found by dividing watts by voltage (and by power factor for AC). Power factor accounts for AC loads where current and voltage aren't perfectly in step; use 1.0 for DC and simple resistive loads like heaters, and around 0.8 for many motors. Once you have amps, size the conductor with our wire size calculator.
How to use this calculator
- Enter the power in watts.
- Enter the circuit voltage.
- Set power factor to 1.0 for DC or resistive loads, or about 0.8 for motors.
- Read the current in amps and the power in kilowatts.
- Use the amps to pick a wire size and breaker.
The formula
This is the single-phase form of Ohm's power law. For DC and resistive AC loads, power factor is 1, so amps is simply watts divided by volts. Motors and electronics have a lower power factor, which raises the current.
Worked example
A 1,000 W resistive load on a 120 V circuit draws 1,000 / 120 = 8.33 A. The same load on a 240 V circuit draws only 4.17 A — higher voltage means lower current for the same power.
Watts to amps at common voltages (PF = 1)
| Watts | 120 V | 240 V |
|---|---|---|
| 500 W | 4.2 A | 2.1 A |
| 1,000 W | 8.3 A | 4.2 A |
| 1,500 W | 12.5 A | 6.3 A |
| 3,000 W | 25.0 A | 12.5 A |
| 5,000 W | 41.7 A | 20.8 A |
Tips & gotchas
- Use 1.0 power factor for heaters, toasters, and incandescent lights.
- Motors and many electronics run around 0.8 — lower power factor, more current.
- Higher voltage means lower current for the same watts, so 240 V circuits use smaller wire.
- Keep continuous loads under 80% of the breaker rating.
- This is single-phase; three-phase uses an extra √3 factor.
Frequently asked questions
How do I convert watts to amps?
Divide watts by volts (and by power factor for AC). A 1,200 W load at 120 V draws 10 A at a power factor of 1.
What is power factor?
It measures how effectively AC current does work. Resistive loads are 1.0; motors and electronics are lower, which increases the current for the same watts.
Why does voltage change the amps?
Power equals volts times amps, so for fixed watts, doubling the voltage halves the current. That's why high-power devices use 240 V.
What about three-phase?
Three-phase adds a factor of the square root of three. This calculator covers DC and single-phase AC.
How does this help with wire size?
Amps drive both wire gauge and breaker size. Convert your watts to amps here, then use the wire size calculator.
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