Power Factor Calculator

Power factor describes how effectively an alternating-current load converts supplied volt-amperes into useful real power. It is the ratio of active power in watts to apparent power in volt-amperes. For the single-phase measurements used here, apparent power equals RMS voltage multiplied by RMS current. Dividing measured active power by that product gives a dimensionless power factor between zero and one. A value near one indicates that most supplied current contributes to real work or heat. Inductive and capacitive loads can shift current relative to voltage. Motors, transformers, fluorescent lighting, and lightly loaded power supplies commonly draw reactive current. That current increases conductor and transformer loading even though it does not deliver net energy over a complete cycle. The calculator uses the power triangle to find reactive power: the square root of apparent power squared minus active power squared. It also finds the magnitude of the phase angle by taking the inverse cosine of power factor. Consider a 120-volt load drawing 10 amperes and consuming 960 watts. Apparent power is 1,200 volt-amperes, so the power factor is 0.8. Reactive power is 720 volt-amperes reactive and the phase-angle magnitude is about 36.87 degrees. These values describe the size of the phase relationship but do not identify whether current leads or lags. That distinction requires knowing whether the load is predominantly capacitive or inductive. This implementation is intended for single-phase circuits. Balanced three-phase systems use apparent power equal to the square root of three times line-to-line voltage times line current. Applying the single-phase formula directly to three-phase line measurements would produce an incorrect result. Distorted waveforms also require true-power and true-RMS instruments because displacement power factor alone does not include harmonic distortion. Power-factor correction commonly adds capacitors near inductive loads to offset reactive demand. Correction can reduce current, voltage drop, losses, and utility demand charges, but equipment must be sized for system voltage, harmonics, switching transients, and resonance. Correcting beyond unity is neither represented by this simple ratio nor generally desirable. Use simultaneous measurements taken under the same operating condition. Active power cannot exceed apparent power in the ideal relationships used by this calculator, so inputs outside that range are rejected. For billing studies, industrial capacitor banks, generators, or safety-critical electrical design, rely on qualified personnel, calibrated power analyzers, and the standards applicable to the installation.