Watts, Volts and Amps Calculator
Pick what to solve for, enter the other two values, and get the answer using power = voltage × current.
How it works
Watts = volts × amps. Amps = watts ÷ volts. Volts = watts ÷ amps. Kilowatts = watts ÷ 1,000. In SI units one volt is one watt per ampere (NIST SP 330), which is where P = V × I comes from.
Worked example: Solving for watts: 240 V × 30 A = 7,200 W = 7.2 kW, which matches DOE AFDC's figure for residential Level 2 chargers. Solving for amps: 1,500 W ÷ 120 V = 12.5 A.
Assumptions
- Watts = volts × amps exactly. This holds for DC and for AC loads with a power factor of 1 (purely resistive, such as heaters). Many AC devices with motors or electronics draw more volt-amperes than watts; use the device's nameplate rating.
- Single-phase only. Three-phase circuits use a different formula and are not covered.
- Nominal voltage (for example 120 V or 240 V). Actual line voltage varies slightly.
- This tool does not size wires, breakers or circuits. For installation questions, use a licensed electrician.
Frequently asked questions
How many amps is 7.2 kW at 240 volts?
7,200 W ÷ 240 V = 30 A. The U.S. DOE Alternative Fuels Data Center says most residential Level 2 EV chargers operate at up to 30 amps, delivering 7.2 kW.
How do I convert watts to amps?
Divide watts by volts. For example, 1,500 W ÷ 120 V = 12.5 A. A U.S. DOE/NREL fact sheet states the same relationship: watts = amps × volts.
How do I convert amps to kW?
Multiply amps by volts and divide by 1,000. At 240 V, 40 A × 240 = 9,600 W = 9.6 kW.
Related calculators
- EV charger amps to kW chart
- EV charger power and miles-per-hour calculator
- kW to kWh calculator
- Amp-hours to kWh battery calculator
Sources
Formulas and reference values are from these sources. Page last reviewed 2026-10-19.