Electrical Power Calculator
Calculate electrical power in watts using voltage, current, or resistance with three formulas.
Estimates for planning only — verify against local electrical codes and a qualified professional before installation.
How it works
- 1Choose the method: Voltage × Current, Current² × Resistance, or Voltage² ÷ Resistance.
- 2Enter the two known quantities — voltage (V), current (A), or resistance (Ω).
- 3The result is shown in watts, with kilowatt and horsepower conversions.
Use cases
- Sizing circuit breakers and fuses for household and industrial loads.
- Calculating heat dissipation in resistors and electronic components.
- Comparing motor and appliance power ratings across unit systems.
Frequently asked questions
Which power formula should I use?
Use P = V·I when you know voltage and current. Use P = I²·R for a known current and resistance, and P = V²/R for a known voltage and resistance.
Can you show a worked example?
A kettle at 230 V drawing 13 A: P = 230 × 13 = 2990 W ≈ 3 kW, or about 4 hp — a handy cross-check against the rating plate.
Why does P = V²/R return — for zero resistance?
A short circuit (R = 0 Ω) gives division by zero, which is undefined. The calculator shows — to flag a non-physical input.
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