Watt Calculator
Power in watts from voltage and current — the number on your electricity bill's per-appliance breakdown, and the first check before assuming a circuit, fuse, or extension cord can handle a given load.
Inputs
Result
1,150 W
1.15 kW
How it works
P = V × I
How the watt calculator works
P = V × I, in watts when V is in volts and I is in amps.
Divide by 1,000 for kilowatts, the unit electricity is typically billed in.
Worked example: 230 V mains, 5 A draw
- P = 230 × 5 = 1,150 W.
- In kilowatts: 1,150 ÷ 1,000 = 1.15 kW.
Common mistakes to avoid
Using nameplate current for a motor or compressor's running power
Motors often draw a much higher inrush current briefly at startup than their steady running current — using the startup figure overstates continuous power draw significantly.
Confusing watts with volt-amps for AC loads with poor power factor
For non-resistive AC loads (motors, some electronics), V × I gives apparent power (VA), not necessarily real power in watts — the Power Factor Calculator bridges that gap.
Frequently asked questions
How do I convert watts to the units on my electricity bill?
Electricity is billed in kilowatt-hours (kWh) — multiply the power in kW by the hours used to get the energy consumed, which is what's actually billed.
Why does my appliance's power rating differ from V × I on its nameplate?
For AC devices with a power factor below 1 (common in motors), the nameplate volts × amps is apparent power, while actual power drawn is lower — multiply by the power factor to reconcile the two.
What's a safe current draw for a standard household circuit?
This varies heavily by country and circuit rating (commonly 13-20 A per circuit) — check your specific circuit breaker or fuse rating rather than assuming a universal figure.
How is this different from the Power Calculator?
This one uses electrical inputs (voltage and current); the Power Calculator instead computes power from mechanical work done over time — same unit, different starting quantities.
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