Volts to watts calculator
Volts alone cannot give you watts. You also need the current the load draws (or its resistance). Enter voltage and amps below.
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
Can you convert volts to watts directly?
No. Watts are volts multiplied by amps (and power factor for AC). Without the current, or the resistance of the load, there is no answer.
How many watts is 12 volts?
It depends on current: 12 V at 5 A is 60 W; 12 V at 10 A is 120 W.
How do I get watts from volts and ohms?
P = V² ÷ R. 12 V across a 6 Ω load is 144 ÷ 6 = 24 W.