Power and energy
Kilowatt-hours from V and I
- where
- energy (kWh)
- voltage (V)
- current (A)
- duration (h)
Explain this equation
Works out energy in kWh from voltage, current and running time. Useful when you have a clamp reading rather than a rating.
E(kWh) is the energy used. V × I gives the power in watts. t(h) is the running time in hours.
V × I gives watts, dividing by 1000 turns that into kilowatts, and multiplying by hours gives kilowatt-hours.
Sense check: 230 V at 10 A is 2.3 kW, so 2 hours uses 4.6 kWh. Halve the current and the energy halves.
Watch out: time must be in hours here. On AC loads that are not purely resistive, V × I overstates real energy unless power factor is near one.
Calculate watts from voltage and current, convert to kilowatts and multiply by hours. This combines two familiar relationships.
A motor’s mechanical output is not its electrical input. AC loads may need power factor and efficiency information before using a rating.
Enter your values to see the result.
Common mistake
Using seconds in this hours-based version.
Limits
Steady DC or unity-power-factor AC.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.