How to convert watts, amps and volts
Power (watts) equals voltage times current. On AC circuits with motors or electronics, multiply by the power factor too, and on three-phase circuits multiply by √3 (1.732).
DC: P = V × I
AC 1-phase: P = V × I × PF
AC 3-phase: P = 1.732 × V × I × PF
Amps: I = P ÷ (V × PF) (1-phase)
Examples
- 1,500 W space heater on 120 V: 1500 ÷ 120 = 12.5 A
- Air conditioner drawing 15 A at 240 V, PF 0.9: 240 × 15 × 0.9 = 3,240 W
- 10 kW three-phase motor at 480 V, PF 0.85: 10000 ÷ (1.732 × 480 × 0.85) = 14.2 A
Watts to amps at 120 V and 240 V
| Watts | Amps at 120 V | Amps at 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 |
| 2,000 W | 16.7 A | 8.3 A |
| 3,000 W | 25 A | 12.5 A |
| 5,000 W | 41.7 A | 20.8 A |
Frequently asked questions
How many amps is 1,500 watts?
12.5 amps at 120 V, or 6.25 amps at 240 V.
How many watts can a 15 amp circuit handle?
1,800 W at 120 V in theory, but continuous loads should stay under 80%, or 1,440 W.
What is power factor?
The ratio of real power (watts) to apparent power (volt-amps). Resistive loads like heaters have PF 1.0; motors and power supplies are usually 0.7–0.95.