What this calculator does
AC power & power factor works out real, reactive and apparent power in an AC circuit from RMS values and phase angle. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaP=VI·cosφ; Q=VI·sinφ; S=VI; power factor = cosφ = P/S; S² = P² + Q²
The inputs explained
| Field | What to enter |
|---|---|
| RMS voltage (V) | A number, measured in V. Starts at 230. |
| RMS current (A) | A number, measured in A. Starts at 5. |
| Phase angle (V leads I) (°) | A number, measured in °. Starts at 30. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with rms voltage
Every other input is held at the calculator’s starting values while rms voltage varies. Select any row to load that scenario into the calculator.