Power Factor Calculator

See how active power factor correction reshapes the input current waveform. Adjust the phase angle and toggle PFC on or off — the widget plots voltage, current, and instantaneous power while reporting PF, true power, and apparent power live.

V_rms: 230 VP_load: 250 W

THD_i (uncorrected): 150 %

φ (displacement): 0 °

Waveforms normalized for shape comparison — voltage and current amplitudes are not to the same scale

Power Factor

0.555

Displacement PF

1.000

\small \cos(0^\circ) = 1.000

Distortion PF

0.555

\small \tfrac{1}{\sqrt{1+1.50^2}} = 0.555

Combined Power Factor

\small PF = \cos\varphi \cdot \tfrac{1}{\sqrt{1+THD_i^2}} = 1.000 \times 0.555 = 0.555

THD_i = 150% = 1.50 (decimal)

$I_{rms}$ (drawn from mains)

1.96 A

$S$ (Apparent power)

450.7 VA

$P$ (Real power)

250.0 W

Extra current wasted

44.5% of apparent power is non-useful

Quick experiments

Default diode bridge. With the default settings the power factor reads around 0.55 — a typical uncompensated rectifier load.
Toggle PFC on. Enable active PFC and watch the current snap into phase with voltage, pushing PF close to unity.
Phase lag without PFC. Set φ = 30° with PFC off — the displacement drops PF to cos 30° ≈ 0.87, and the power waveform dips negative each cycle.

Power factor in AC circuits

Power factor (PF) is the ratio of real power P (watts) to apparent power S (volt-amperes): PF = P / S = cos(φ), where φ is the phase angle between voltage and current. A PF of 1.0 means all supplied energy does useful work; lower PF means the grid must supply more current for the same useful power.

Real, reactive, and apparent power

P (W): real power — does actual work (heat, motion, light).
Q (VAR): reactive power — stored and returned by inductors/capacitors; does no net work but loads cables and transformers.
S (VA): apparent power — S = √(P² + Q²); what the generator and cables must provide.

Power factor correction (PFC)

Adding capacitors in parallel with inductive loads (motors, fluorescent ballasts) cancels reactive current and raises PF toward 1.0. Industrial users are charged by utilities for reactive power when PF drops below 0.95. Switched-mode power supplies use active PFC circuits to maintain near-unity PF.

Learn more → Power Factor Correction — Learn

Formula reference

Power factor: $PF = \dfrac{P}{S} = \cos\phi$
Real power over apparent power. Only equals cos φ for linear loads.
Apparent power: $S = V_{rms} I_{rms}$
Measured in volt-amperes, not watts.
Reactive power: $Q = \sqrt{S^{2} - P^{2}}$
The component that does no useful work, in VAR.
Correction capacitance: $C = \dfrac{Q_c}{2\pi f V^{2}}$
The numerator is the reactive power the capacitor must supply.

Symbol	Meaning	Unit
$P$	Real power	W
$S$	Apparent power	VA
$Q$	Reactive power	VAR
$\phi$	Phase angle between voltage and current	°

Common mistakes

Trying to correct distortion power factor with capacitors.
Capacitors only fix displacement (phase) power factor. Harmonic distortion from rectifiers needs a filter or an active PFC stage.
Over-correcting into a leading power factor.
Too much capacitance swings the load capacitive, which is just as penalised and can resonate with supply inductance.
Assuming a power factor above 1 is possible.
Real power cannot exceed apparent power, so PF ≤ 1. A higher reading means a measurement error.
Confusing kW with kVA when sizing.
Cables, transformers and generators are sized on kVA because they carry the total current. A 0.7 PF load needs about 43 % more VA than its kW figure.
Leaving correction capacitors permanently connected.
At light load a fixed capacitor over-corrects. Switched capacitor banks track the load instead.

Frequently asked questions

What is power factor?

Power factor is the ratio of real power in watts to apparent power in volt-amperes. A power factor of 0.7 means only 70 percent of the current drawn is doing useful work.

What is the difference between displacement and distortion power factor?

Displacement power factor comes from the phase shift between voltage and current in linear loads such as motors. Distortion power factor comes from harmonic current drawn by non-linear loads such as rectifiers, and no amount of capacitance corrects it.

How do I correct a lagging power factor?

Add capacitance in parallel with the inductive load. The capacitor supplies reactive current locally so the supply does not have to, which reduces line current without changing the real power delivered.

Why do utilities charge for poor power factor?

Reactive current still flows through the cables, transformers and switchgear, causing I squared R losses and consuming capacity, even though it does no useful work. Large consumers are billed for it to recover that cost.

Can power factor be greater than one?

No. Real power can never exceed apparent power, so power factor is bounded by 1. A reading above 1 indicates a measurement or instrumentation error.

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