Watts to amps calculator
Enter the load in watts and the supply voltage. For AC motors and electronics, add the power factor from the nameplate for a realistic current.
Quick reference
| Watts | 12 V DC | 120 V | 240 V |
|---|---|---|---|
| 100 W | 8.33 | 0.83 | 0.42 |
| 500 W | 41.67 | 4.17 | 2.08 |
| 1,000 W | 83.33 | 8.33 | 4.17 |
| 1,500 W | 125 | 12.5 | 6.25 |
| 2,000 W | 166.7 | 16.67 | 8.33 |
| 2,500 W | 208.3 | 20.83 | 10.42 |
| 3,000 W | 250 | 25 | 12.5 |
| 4,000 W | 333.3 | 33.33 | 16.67 |
| 5,000 W | 416.7 | 41.67 | 20.83 |
| 7,500 W | 625 | 62.5 | 31.25 |
| 10,000 W | 833.3 | 83.33 | 41.67 |
Amps at power factor 1 (resistive loads).
The formulas
DC: P = V × I, so I = P ÷ V
AC single-phase: P = V × I × PF, so I = P ÷ (V × PF)
AC three-phase: P = 1.732 × VLL × I × PF, so I = P ÷ (1.732 × VLL × PF)
PF is power factor, between 0 and 1. Resistive loads (heaters, incandescent lamps, water heaters) are 1. Motors, compressors and power supplies are lower, which means they draw more current for the same watts.
Using the result safely
- Nameplate current beats a calculation. If the equipment lists amps, use that figure.
- For a load that runs 3 hours or more (EV charger, water heater, space heater), the NEC sizes conductors and breakers at 125% of the load.
- To pick the conductor for the current you found, go to the wire size calculator; for long runs check the voltage drop.
Questions people ask
How many amps is 1500 watts?
12.5 A at 120 V (1500 ÷ 120) and 6.25 A at 240 V. A 1500 W space heater is treated as a continuous load, so it needs a circuit rated at least 12.5 × 1.25 = 15.6 A, which is why they belong on a 20 A circuit.
How many amps is 1000 watts?
8.33 A at 120 V, 4.17 A at 240 V, and 83.3 A at 12 V DC.
What formula converts watts to amps?
DC: I = P ÷ V. Single-phase AC: I = P ÷ (V × PF). Three-phase AC: I = P ÷ (√3 × V × PF), with V the line-to-line voltage.
What power factor should I use?
Use 1.0 for resistive heaters and incandescent lighting. Motors typically run 0.8 to 0.9 at full load; check the nameplate. Unknown electronics: 0.9 is a cautious starting point.