Amps to watts calculator
Enter current and voltage to get real power in watts. The panel also shows how much continuous load a breaker of that size is meant to carry.
Quick reference
| Amps | 12 V DC | 120 V | 240 V | 80% at 120 V |
|---|---|---|---|---|
| 1 A | 12 | 120 | 240 | 96 |
| 5 A | 60 | 600 | 1,200 | 480 |
| 10 A | 120 | 1,200 | 2,400 | 960 |
| 15 A | 180 | 1,800 | 3,600 | 1,440 |
| 20 A | 240 | 2,400 | 4,800 | 1,920 |
| 30 A | 360 | 3,600 | 7,200 | 2,880 |
| 40 A | 480 | 4,800 | 9,600 | 3,840 |
| 50 A | 600 | 6,000 | 12,000 | 4,800 |
| 60 A | 720 | 7,200 | 14,400 | 5,760 |
| 100 A | 1,200 | 12,000 | 24,000 | 9,600 |
Watts at power factor 1. The last column is the continuous load a 120 V breaker of that size is meant to carry.
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 watts is 15 amps?
1,800 W at 120 V. For a load running 3 hours or more, NEC 210.20(A) sizes the breaker at 125% of the load, which works out to 1,440 W continuous on a 15 A, 120 V circuit.
How many watts can a 20 amp circuit handle?
2,400 W at 120 V, or 1,920 W continuous. At 240 V it is 4,800 W, or 3,840 W continuous.
What is the amps to watts formula?
DC: P = V × I. Single-phase: P = V × I × PF. Three-phase: P = √3 × V × I × PF.