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Electrical Power Calculator

Calculate electrical power, voltage, current and resistance from a known pair of values, with optional energy use in kWh over a run time.

These are ideal-circuit educational calculations; real component tolerance, temperature and parasitic effects are not modeled.

How to use

This electrical power calculator links voltage, current, resistance and power for an ideal resistive load. Choose the pair you know and it solves the other two values; an optional run time estimates energy use in kWh.

  1. Choose which two quantities are known.
  2. Enter the required values.
  3. Optionally enter operating hours.
  4. Review power and derived values.

How it is calculated

P=VI=I²R=V²/R; energy kWh=(P/1000)×hours

Example

Example: 12 V and 2 A gives 24 W and 6 Ω. Over 5 hours, idealized energy use is 0.12 kWh.

Important notes

The model assumes a resistive load. In AC with reactance or power factor, real power can differ from V×I.

Frequently asked questions

Is P=V×I always real power?

For DC or an ideal resistive load yes; general AC can require power factor.

How is kWh calculated?

Convert watts to kilowatts and multiply by hours.

What resistance is shown?

The equivalent resistance implied by the entered values.