P=VIElectrical Power Calculator
Electrical power is the rate at which electrical energy is transferred or converted. The three equivalent power formulas (P = VI, P = I²R, P = V²/R) allow power to be calculated from any two of the three fundamental quantities (V, I, R). Power is measured in watts (W), where 1 watt = 1 joule per second.
- 1P = V × I (power = voltage × current)
- 2P = I² × R (useful when voltage is unknown)
- 3P = V² / R (useful when current is unknown)
- 4Energy consumed: E = P × t (joules = watts × seconds)
- 5kWh (unit on electricity bills) = kilowatts × hours
230 V, 10 A circuit=P = 230 × 10 = 2,300 W = 2.3 kW10-amp ring main in a UK home
2 Ω resistor, 5 A current=P = I²R = 25 × 2 = 50 W
3 kW kettle running for 3 minutes=Energy = 3 × (3/60) = 0.15 kWh ≈ 4p at 25p/kWh
| Appliance | Power (W) | Units/hour at 25p/kWh |
|---|---|---|
| Kettle | 2,000–3,000 W | 50–75p |
| Electric shower | 7,500–10,500 W | £1.88–2.63 |
| Washing machine | 1,200–2,400 W | 30–60p |
| Laptop | 20–100 W | 0.5–2.5p |
| LED bulb | 5–15 W | ~0.3p |
| Electric car charging (fast) | 7,200–22,000 W | £1.80–5.50 |
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