Free Electrical calculator

kW, kVA, kVAr and power-factor calculator

Complete the power triangle from kW and power factor, kVA and power factor, or kW and kVA.

Enter the project values

All values remain in your browser. Review the assumptions before using the result.

Your result will appear here.Calculate to see the outputs, formula and substituted working.

How the calculation works

Right-angle power triangle using positive magnitudes.

Formula

PF = P ÷ S; Q = √(S² − P²)

Worked example

Real power100 kW

Power factor0.80

Expected apparent power125 kVA

Expected reactive power75 kVAr

Assumptions and limitations

Assumptions

Values are steady-state RMS quantities.
Reactive power is reported as a positive magnitude.

What this does not check

Does not identify leading or lagging sign.
Does not model distortion power or select correction equipment.

Formula version: 1.0 · Last reviewed: 16 August 2026

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Engineering basis: first-principles electrical relationships using user-entered values. The page does not reproduce BS 7671 tables or establish compliance. Complete the project-specific design against the current BS 7671 information, manufacturer data and the applicable project requirements.

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