Watts to Amps Calculator
Enter the power in watts and the supply voltage to find the current in amps. Choose DC, single-phase or three-phase AC, and set a power factor for motors and other reactive loads.
Amps measure the flow of electric current, while watts measure power — the rate at which energy is used. To turn a wattage into a current you also need the voltage, because the same power draws a smaller current at a higher voltage. For alternating-current circuits with motors, transformers or other reactive loads, a power factor between 0 and 1 corrects for the difference between apparent and real power. This calculator handles all three common cases.
How to convert watts to amps
The formula depends on whether the supply is direct current, single-phase alternating current, or three-phase. In each case you divide power by voltage, then adjust for power factor and, for three-phase, the square root of three.
AC single-phase: Amps = Watts ÷ (Volts × PF)
AC three-phase: Amps = Watts ÷ (√3 × Volts × PF)
| Circuit | Formula | Example (1500 W) |
|---|---|---|
| 12 V DC | 1500 ÷ 12 | 125 A |
| 120 V single-phase | 1500 ÷ (120 × 1.0) | 12.5 A |
| 240 V single-phase | 1500 ÷ (240 × 1.0) | 6.25 A |
| 400 V three-phase, PF 0.8 | 1500 ÷ (1.732 × 400 × 0.8) | 2.71 A |
Worked example
A 1500-watt space heater on a 120-volt single-phase outlet with a power factor of 1.0 (pure resistive heating):
| Amps = 1500 ÷ (120 × 1.0) | 12.5 A |
| Continuous load ÷ 0.8 = 12.5 ÷ 0.8 | 15.6 A |
| Next common breaker size | 20 A |
Because the heater runs continuously, code requires the circuit to be rated for at least 125% of the load, so a 20-amp circuit is appropriate even though the draw is only 12.5 amps.
What power factor should I use?
Power factor describes how effectively current is converted to useful work. Purely resistive loads — incandescent bulbs, heaters, kettles — have a power factor of 1.0. Motors, fluorescent and LED drivers, and other inductive loads typically run between 0.7 and 0.95. If you don't know the exact figure, 0.8 is a common assumption for motor circuits, while 1.0 is safe for heating and lighting. Using a lower power factor increases the calculated current, so it errs on the cautious side.
Single-phase vs three-phase
Homes and small workshops are almost always single-phase. Three-phase supplies are found in larger commercial and industrial settings and deliver the same power at a lower current per conductor, which is why the three-phase formula includes the √3 (about 1.732) factor. Be sure to pick the right option, because the current for a given wattage can differ by a factor of two or more between phases.