Volts to Watts Calculator
Enter voltage and current below — the watts update instantly.
How do you convert volts to watts?
Multiply volts by amps: W = V × A. A device at 120 V drawing 5 A uses 120 × 5 = 600 W. Voltage alone cannot give watts — you need the current too. For AC single-phase, include the power factor: W = V × A × PF, so 120 V at 5 A with PF 0.9 gives 120 × 5 × 0.9 = 540 W.
Volts to Watts Formula
Power is simply voltage times current. Example: a 12 V circuit carrying 2 A delivers 12 × 2 = 24 W.
Real power on AC is scaled by the power factor. A resistive heater sits near PF 1.0; motors and switch-mode supplies run lower.
The √3 factor (≈ 1.732) applies to balanced three-phase loads. Use the line-to-line voltage (e.g. 400 V or 480 V).
Common Volts to Watts Values (DC / PF 1.0)
| Voltage | at 1 A | at 5 A | at 10 A | at 20 A |
|---|---|---|---|---|
| 12 V | 12 W | 60 W | 120 W | 240 W |
| 24 V | 24 W | 120 W | 240 W | 480 W |
| 120 V | 120 W | 600 W | 1,200 W | 2,400 W |
| 230 V | 230 W | 1,150 W | 2,300 W | 4,600 W |
| 240 V | 240 W | 1,200 W | 2,400 W | 4,800 W |
Designing Heating Elements (V² / R)
The Volts to Watts formula (W = V² ÷ R) is uniquely useful because it lets you calculate power output based on a component's physical resistance. Since resistance doesn't change easily, voltage is the driving factor. Notice how sensitive the power output is to voltage changes:
| Scenario (Same 10 Ω Heater Element) | Voltage Applied | Power Output (Watts) |
|---|---|---|
| Used correctly on 120V US outlet | 120 V | (120 × 120) ÷ 10 = 1,440 W |
| During a severe "brownout" | 100 V | (100 × 100) ÷ 10 = 1,000 W (30% less heat) |
| Accidentally plugged into a 240V European outlet | 240 V | (240 × 240) ÷ 10 = 5,760 W (Catastrophic failure) |
Because voltage is squared in the formula, a small drop in utility voltage causes a massive drop in heating power. Conversely, doubling the voltage quadruples the power, immediately melting the element.
Frequently Asked Questions
How do I convert volts to watts?
Multiply voltage by current: W = V × A. For AC single-phase: W = V × A × PF. For three-phase: W = √3 × V × A × PF. You need the current as well — voltage on its own cannot give watts.
Can I convert volts to watts without amps?
No — watts is volts times amps, so the current is required. If you only know resistance, first find current with Ohm's Law (A = V ÷ R), then apply W = V × A.
How many watts is 120 volts?
It depends on the current the device draws. At 120 V: 1 A = 120 W, 5 A = 600 W, 12.5 A = 1,500 W. Enter the current above for an exact figure.
What is the difference between volts and watts?
Volts measure electrical pressure; watts measure power. Since W = V × A, a high voltage at low current can deliver the same wattage as a low voltage at high current. See watts vs amps for more.
Why does my space heater output less heat during high-demand winter days?
During high-demand periods, utility grid voltage can sag (a brownout). Because heating power equals Voltage squared divided by Resistance (W = V² ÷ R), a 10% drop in voltage (from 120V to 108V) results in a nearly 20% drop in heat output from a purely resistive space heater.