Amps to Watts Calculator
Enter the current in amps and the supply voltage to find the power in watts. Choose DC, single-phase or three-phase AC, and set a power factor for motors and other reactive loads.
Watts measure real power — the rate at which energy is actually used — while amps measure the current flowing through a circuit. To turn a current into a power figure you also need the voltage, and for alternating-current circuits with motors or electronics you apply a power factor to account for the gap between apparent and real power. This calculator covers DC, single-phase and three-phase supplies.
How to convert amps to watts
Multiply current by voltage, then apply the power factor and, for three-phase circuits, the square root of three. It is the inverse of converting watts to amps.
AC single-phase: Watts = Amps × Volts × PF
AC three-phase: Watts = √3 × Amps × Volts × PF
| Circuit | Formula | Example (10 A) |
|---|---|---|
| 12 V DC | 10 × 12 | 120 W |
| 120 V single-phase | 10 × 120 × 1.0 | 1200 W |
| 240 V single-phase | 10 × 240 × 1.0 | 2400 W |
| 400 V three-phase, PF 0.8 | 1.732 × 10 × 400 × 0.8 | 5543 W |
Worked example
A motor drawing 16 amps on a 400-volt three-phase supply with a power factor of 0.8:
| Watts = 1.732 × 16 × 400 × 0.8 | 8868 W |
| In kilowatts | 8.87 kW |
| Apparent power = 1.732 × 16 × 400 | 11085 VA |
The real power is about 8.87 kW, while the apparent power the supply must deliver is around 11.1 kVA — the difference is what the 0.8 power factor represents.
Real power, apparent power and power factor
In AC circuits, current and voltage don't always peak together. Real power (watts) is the energy that does useful work; apparent power (volt-amps) is what the supply has to provide; and power factor is the ratio between them. Resistive loads such as heaters and incandescent lamps have a power factor of 1.0, so watts and volt-amps are equal. Motors and many electronic devices sit lower, typically 0.7 to 0.95, meaning they draw more current than their wattage alone would suggest.
Single-phase vs three-phase
Most homes and small workshops run on single-phase power, while larger commercial and industrial sites use three-phase, which carries more power for a given current per conductor. The three-phase formula therefore includes the √3 (roughly 1.732) factor. Choosing the wrong supply type will throw the result off substantially, so confirm which one your circuit uses before you calculate.