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Electric Power Calculator
Calculate electric power, energy use and running cost from voltage, current, resistance and hours.
Power, energy and cost
Power: —
Energy: —
Estimated cost: —
How to use the Electric Power Calculator
- Pick the power formula that matches the values you know.
- Enter voltage, current, resistance, hours of use and the price per unit.
- Read the power in watts, the energy in kilowatt hours and the estimated cost.
Features
- Three power formulas including voltage and resistance
- Energy converted to kilowatt hours
- Running cost from your own price per unit
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online electric power calculator.
Power in watts equals voltage in volts multiplied by current in amperes, written as P = V × I
for a direct current circuit.
Enter the hours of use and the price per kilowatt hour. The tool multiplies power by time to
get energy, then energy by the rate.
A kilowatt hour is the energy used by a one kilowatt appliance running for one hour, and it
is the unit on your electricity bill.
Yes. Switch the formula to P = V² / R and enter the voltage and the resistance in ohms to get
the power in watts.
Power equals current squared multiplied by resistance, so doubling the current quadruples the
power dissipated as heat.
One kilowatt equals one thousand watts, so a 1150 watt appliance uses 1.15 kilowatts of power
while it is running.
Yes. Enter the price per kilowatt hour in your own currency and the cost is shown in the same
currency units.
No. All calculations happen locally in your browser and nothing you type is uploaded or
stored.
Yes. The electric power calculator is completely free and unlimited, with no account needed.
Last updated: October 10, 2026