Electrical power calculator (watts)
Pick the supply type, enter voltage and current, plus power factor for AC, and get real and apparent power.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter supply type, voltage, current and power factor (ac).
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
DC: P = V × I. Single-phase: P = V × I × PF. Three-phase: P = √3 × V × I × PF with V the line voltage. Apparent power S = V × I or √3 × V × I.
Example
Inputs: Supply type = AC single-phase, Voltage = 230 V, Current = 10 A, Power factor (AC) = 0.8. Result: Real power: 1,840 W; Power in kilowatts: 1.84 kW; Apparent power: 2,300 VA.
Limits and caveats
- For three-phase, enter the line-to-line voltage (such as 400 V), not the phase voltage.
- Power factor is ignored for DC.
- Motor and air conditioner inrush current is higher than running current and is not included.
Questions about this tool
What is power factor and what should I enter?
It is the ratio of real to apparent power. Heaters and incandescent lamps are close to 1; motors are usually 0.8 to 0.9. Check the rating plate if you are unsure.
What is the difference between watts and volt-amperes?
Watts are real power turned into work or heat; volt-amperes are voltage times current. They are equal only when the power factor is 1.
Why does √3 appear for three-phase?
In a balanced system the line voltage equals the phase voltage times √3, so total power is √3 × line voltage × current × PF.