Volts to Watts Calculator
Volts alone do not tell you watts — you also need the current or the resistance. Enter the voltage plus either one to calculate the power.
How to use the Volts to Watts Calculator
- Enter the voltage.
- Choose whether you know the current (amps) or the resistance (ohms).
- Enter that value to get the power in watts.
How it works
Power is voltage times current: P = V × I. If you know the resistance instead, substitute Ohm’s law (I = V ÷ R) to get P = V² ÷ R. A 12 Ω heating element on 120 V draws 10 A and uses 120² ÷ 12 = 1,200 W.
These formulas are exact for DC and for resistive AC loads. For motors and electronics on AC, multiply by the power factor.
Watts at common voltages
| Current | 12 V | 120 V | 240 V |
|---|---|---|---|
| 1 A | 12 W | 120 W | 240 W |
| 2 A | 24 W | 240 W | 480 W |
| 5 A | 60 W | 600 W | 1,200 W |
| 10 A | 120 W | 1,200 W | 2,400 W |
| 15 A | 180 W | 1,800 W | 3,600 W |
| 20 A | 240 W | 2,400 W | 4,800 W |
Frequently asked questions
How many watts is 120 volts?
It depends on the current: at 10 A it is 1,200 W; at 15 A, 1,800 W.
How do I convert volts to watts without amps?
You need the resistance instead: P = V² ÷ R.
How many watts is 12 volts at 5 amps?
60 W.
Are volts and watts the same?
No. Volts measure electrical pressure, amps measure flow and watts measure power — the rate energy is used.