Power factor tells you how efficiently an AC circuit converts the power a utility supplies into actual useful work. A low power factor means extra current flows for no useful output β€” which shows up as higher demand charges, larger required wiring and transformers, and more heat loss. This calculator computes power factor from real and apparent power (or a phase angle), breaks down the reactive power in the power triangle, and sizes the capacitance needed to correct a low power factor toward a target value.

How the Power Factor Calculator works

On the Power Factor tab, PF = cosΟ† = P/S: the calculator divides real power (P, in watts) by apparent power (S, in volt-amps), or takes the cosine of a phase angle you enter directly. On the Reactive Power tab, it derives Q = √(SΒ² βˆ’ PΒ²) β€” the Pythagorean relationship between the three sides of the power triangle (P along the real axis, Q along the reactive axis, S as the hypotenuse). On the Correction tab, it computes the reactive power a shunt capacitor must supply to move the load from its current phase angle to a target phase angle, Qc = P(tanΟ†1 βˆ’ tanΟ†2), then solves for the capacitance that supplies that much reactive power at the given voltage and frequency: C = Qc / (2Ο€fVΒ²). These are the standard single-phase power-triangle and PF-correction formulas taught in AC circuit analysis and power systems courses.

Inputs and what they mean

Real power (P) is the power actually doing work β€” read it from a nameplate, energy meter, or spec sheet, in W, kW, or MW. Apparent power (S) is voltage Γ— current, in VA, kVA, or MVA; it is always greater than or equal to real power. The phase angle (Ο†) is an alternative way to specify the same relationship when P and S aren't both known. Load type (inductive/lagging vs. capacitive/leading) doesn't change the magnitude of PF, but it does change whether the load needs capacitive or inductive correction β€” most real-world loads (motors, transformers, fluorescent ballasts) are inductive and lagging. On the Correction tab, target PF, voltage, and frequency all directly scale the required capacitance: doubling the voltage quarters the required capacitance for the same reactive power, since capacitive reactive power scales with VΒ².

Limits and edge cases

This calculator models a single-phase (or per-phase) circuit with a linear, sinusoidal load. It does not account for three-phase bank sizing, harmonic distortion (which produces a separate "distortion power factor" component that this tool ignores), or capacitor bank switching transients and resonance risk with existing power-factor-correction equipment β€” all of which a qualified electrician or power engineer should evaluate before installing correction capacitors on a real system. Real power can never exceed apparent power in an ideal circuit, so the calculator rejects inputs where P > S, and the Correction tab requires the target PF to be at or above the current PF (you cannot "correct" toward a worse power factor).