Reactive Power Calculator

About this calculator

In an AC circuit, total power splits into three related quantities that form the power triangle: real power P (measured in watts) does actual work, reactive power Q (measured in VAR) sloshes back and forth into inductive or capacitive loads like motors and transformers without doing net work, and apparent power S (in VA) is their vector sum. This calculator finds Q = V·I·√(1−pf²) — equivalently V·I·sin φ — from voltage, current and power factor (pf = cos φ, the phase angle between voltage and current).

Electrical engineers and plant electricians use reactive power calculations to size power-factor-correction capacitors, since utilities often penalize industrial customers with low power factor through surcharges on their bill. Facility managers, HVAC and motor technicians, and electrical engineering students use it to understand why a circuit's apparent power (what the utility bills for capacity) can exceed the real power actually consumed as useful work.