Volts to Watts Calculator
Volts become watts only when you know the current: watts = volts × amps. 120 V at 12.5 A is 1,500 W.
Sources: BIPM SI Brochure Updated
Result
120 V × 12.5 A = 1,500 W
= 1.5 kW of power
The formula
watts = volts × amps × power factor
Voltage alone says nothing about power. A 12-volt car battery and a small 12-volt power adapter have the same voltage and deliver very different power, because the current differs. Power in watts is voltage multiplied by current.
The formula is exact for direct current. For alternating current it is exact when the power factor is 1, and otherwise the product is multiplied by the power factor.
Worked example
- A device draws 12.5 A from a 120 V supply.
- Multiply: 120 × 12.5 = 1,500 W, which is 1.5 kW.
- The other way: a 2,000 W kettle on 230 V draws 2,000 ÷ 230 = 8.7 A.
Watts at common voltages and currents
| Current | 12 V | 24 V | 120 V | 230 V |
|---|---|---|---|---|
| 0.5 A | 6 W | 12 W | 60 W | 115 W |
| 1 A | 12 W | 24 W | 120 W | 230 W |
| 2 A | 24 W | 48 W | 240 W | 460 W |
| 5 A | 60 W | 120 W | 600 W | 1,150 W |
| 10 A | 120 W | 240 W | 1,200 W | 2,300 W |
| 13 A | 156 W | 312 W | 1,560 W | 2,990 W |
| 15 A | 180 W | 360 W | 1,800 W | 3,450 W |
| 16 A | 192 W | 384 W | 1,920 W | 3,680 W |
| 20 A | 240 W | 480 W | 2,400 W | 4,600 W |
Power factor 1. To turn watts into the kilowatt-hours on an electricity bill, see watts to kilowatts.
Frequently asked questions
How many watts is 120 volts?
That cannot be answered without the current. At 1 amp, 120 V is 120 W; at 10 amps it is 1,200 W; at 15 amps it is 1,800 W. Watts = volts × amps.
How do I convert watts to amps?
Divide the watts by the volts. A 1,500 W heater on 120 V draws 1,500 ÷ 120 = 12.5 A. Choose “Amps” under “Solve for” to do it here.
What is the power factor?
For alternating current, the power factor is the share of volts × amps that does real work. It is 1 for a purely resistive load such as a heater or an incandescent lamp, and lower for loads such as motors. Real power in watts = volts × amps × power factor. If you do not know it, the rated wattage on the device's label is more reliable than a calculation.
Does this work for three-phase power?
Not directly. For a balanced three-phase supply the formula is watts = √3 × line-to-line volts × amps × power factor (√3 is about 1.732). This calculator covers direct current and single-phase alternating current.
Are volts and watts the same kind of unit?
No. Volts measure electrical potential, amps measure current and watts measure power, the rate at which energy is used. A volt is defined as one watt per ampere.
Sources
- BIPM, The International System of Units (SI Brochure), 9th edition — the volt is defined as one watt per ampere, so W = V × A