How to Calculate Electric Power
What is Electric Power?
Electric power is the rate at which electrical energy is transferred or consumed. P = V × I (voltage × current), and by Ohm's law can also be expressed as P = I²R or P = V²/R. Measured in watts (W) or kilowatts (kW).
Step-by-Step Guide
- 1P = V × I (Power = Voltage × Current)
- 2P = I² × R (using resistance and current)
- 3P = V² / R (using resistance and voltage)
- 4Energy consumed: kWh = kW × hours; cost = kWh × tariff rate
Worked Examples
Input
230V supply · 5A current
Result
Power = 1,150W (1.15 kW)
230 × 5 = 1,150
Input
2kW heater on 4 hours · 28p/kWh tariff
Result
Cost = £0.56 (56p)
2 × 4 × 0.28 = £2.24/day if 4hr/day