AC Power Calculator
Calculate real, apparent and reactive AC power from voltage, current and power factor.
About AC Power Calculator
The power triangle relates apparent, real and reactive power. Only real power does useful work, but cables and transformers must be sized for apparent power, which is why a poor power factor costs capacity. Utilities charge for kVA capacity as well as kWh consumed, so improving power factor reduces billing even though the useful work is unchanged.
Formula
AC Power
S = V I; P = S cos φ; Q = S sin φ
- S
- Apparent power in volt-amperes
- P
- Real power in watts
- Q
- Reactive power in VAR
Worked example
With the default values below, AC Power Calculator returns Real Power of 2,932.50. Change any input above and every figure here is recalculated in your browser.
Inputs used
- RMS voltageminimum 0 V
- 230 V
- RMS currentminimum 0 A
- 15 A
- Power factoraccepts 0.01–1
- 0.85
Results
- Real Power
- 2,932.50 W
- Apparent Power
- 3,450.00 VA
- Reactive Power
- 1,817.40 VAR
- Phase Angle
- 31.788 degrees
- Real Power
- 2.9325 kW
Step by step
- 1Values used
- 2AC Power
- 3Real Power= 2,932.50 W
- 4Apparent Power= 3,450.00 VA
- 5Reactive Power= 1,817.40 VAR
- 6Phase Angle= 31.788 degrees
- 7Real Power= 2.9325 kW
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is AC Power calculated?
S = V I; P = S cos φ; Q = S sin φ The power triangle relates apparent, real and reactive power. Only real power does useful work, but cables and transformers must be sized for apparent power, which is why a poor power factor costs capacity.
Why does AC Power matter?
Utilities charge for kVA capacity as well as kWh consumed, so improving power factor reduces billing even though the useful work is unchanged.
What values do I need to enter?
This calculator takes 3 inputs: RMS voltage, RMS current, Power factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.