Calculate electrical power from voltage and current, current and resistance, or voltage and resistance. This power calculator estimates watts, milliwatts, kilowatts, voltage, current, and resistance using Ohm's Law and electrical power formulas.
Voltage and current:
Enter volts and amps. The calculator uses P = V × I.
Current and resistance:
Enter amps and ohms. The calculator uses P = I² × R.
Voltage and resistance:
Enter volts and ohms. The calculator uses P = V² ÷ R.
A power calculator helps estimate watts when you know voltage, current, or resistance.
It can help with load estimates, component sizing, battery circuits, DC power planning, appliance power checks, resistor wattage, energy estimates, and basic electrical troubleshooting.
Your result shows estimated power, watts, milliwatts, kilowatts, voltage, current, resistance, estimated energy use over the entered hours, formula used, power category, and scenario comparisons.
Use P = V × I when you know voltage and current. Multiply volts by amps to get watts.
Use P = I² × R. Square the current, then multiply by resistance.
Use P = V² ÷ R. Square the voltage, then divide by resistance.
No. Watts measure power at a moment in time. Kilowatt-hours measure energy used over time.