Single Phase Power Calculator

Work out single-phase AC power in one place. Enter the supply voltage, the power factor and any one of current, real power (kW) or apparent power (kVA), and this calculator returns real power P, apparent power S, reactive power Q and the line current — the full power triangle for a single-phase circuit.

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How to use this calculator

Enter Values

Voltage V (V)

Power factor pf (0–1, default 1.0)

Current I (A) — enter ONE of I / P / S

Real power P (kW) — enter ONE of I / P / S

Apparent power S (kVA) — enter ONE of I / P / S

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter the supply voltage V in volts (e.g. 230 V for a typical single-phase outlet).
Enter the power factor pf between 0 and 1 (leave blank for 1.0 if the load is purely resistive, like a heater).
Enter EXACTLY ONE of current I (amps), real power P (kW) or apparent power S (kVA); the calculator solves the other quantities for you.

How it works

Apparent power is the voltage times the current: S = V·I, divided by 1000 to give kVA. Real power — the part that does useful work — is S scaled by the power factor: P = S·pf (kW). Reactive power, the energy that sloshes back and forth in the load's inductance or capacitance, closes the power triangle: Q = √(S² − P²) in kVAR. If you enter P or S instead of current, the tool rearranges these same relationships to back out the missing values, including the line current I = S·1000 / V.

Worked example

Worked example. A 230 V single-phase load draws 10 A at a power factor of 0.9. Apparent power S = 230 × 10 / 1000 = 2.3 kVA. Real power P = 2.3 × 0.9 = 2.07 kW. Reactive power Q = √(2.3² − 2.07²) = 1.003 kVAR. So the load does 2.07 kW of useful work while the supply must provide 2.3 kVA.

Common mistakes

Entering more than one of current, real power and apparent power — enter just one; the calculator derives the rest.
Confusing kW (real power) with kVA (apparent power). They are only equal when the power factor is 1; at pf 0.9 the kVA is always larger than the kW.
Using this single-phase tool for a three-phase load. Three-phase power needs the √3 factor — use the three-phase power calculator instead.

Frequently asked questions

What is the difference between kW, kVA and kVAR?

kW (real power) is the power that does useful work. kVA (apparent power) is the voltage-times-current the supply must actually deliver. kVAR (reactive power) is the non-working power exchanged with the load's magnetic or electric fields. They form a right triangle: kVA² = kW² + kVAR², and power factor = kW / kVA.

What power factor should I use?

Use 1.0 for a purely resistive load such as a heater or incandescent lamp. Motors, transformers and many electronic supplies run lower — commonly 0.7 to 0.95. If you know the load's power factor from its nameplate, enter it; otherwise the default of 1.0 gives the resistive-load case where kW equals kVA.

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Tip: Enter any known values to calculate the remaining results.

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