Power Factor Calculator

Q: What is power factor?

Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). It ranges from 0 to 1. A PF of 1 means all power is used efficiently. A PF below 0.9 wastes energy and stresses electrical systems.

Q: How do I calculate power factor?

Three methods: (1) PF = kW ÷ kVA. (2) PF = P ÷ √(P² + Q²) where P is real power and Q is reactive power. (3) PF = cos(phase angle in degrees).

Q: What is a good power factor?

A power factor above 0.90 is generally considered good. Industrial facilities are often billed penalties for PF below 0.85–0.90. Unity (PF=1) is ideal but rarely achieved in practice.

Calculate power factor from kW and kVA, from real and reactive power, or from the phase angle. Includes a quality rating for your result.

Calculate Power Factor

Calculation Method

Real Power (kW)

Apparent Power (kVA)

Real Power P (W or kW)

Reactive Power Q (VAR or kVAR)

Phase Angle (degrees, 0–89.9°)

Result

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Power Factor

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Phase Angle

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Rating

Formulas

From kW and kVA:

PF = kW ÷ kVA

From Real Power (P) and Reactive Power (Q):

PF = P ÷ √(P² + Q²)

From Phase Angle (θ):

PF = cos(θ)

Power Factor Rating Guide

Unity (PF = 1.0): Ideal — purely resistive loads. All apparent power is real power.
Good (PF ≥ 0.90): Efficient. Minimal reactive losses. Target for most installations.
Acceptable (PF 0.80–0.90): Common in light industrial. May incur utility penalties.
Poor (PF < 0.80): Wasted energy, higher bills, potential equipment damage. Consider power factor correction capacitors.

Frequently Asked Questions

What is power factor?

Power factor is the ratio of real power (kW) to apparent power (kVA). It measures how efficiently electrical power is used. PF = 1.0 means 100% efficient. Lower values mean current is flowing without doing useful work, wasting energy and increasing costs.

How do I calculate power factor?

Three methods: (1) PF = kW ÷ kVA — simplest if you know both. (2) PF = P ÷ √(P²+Q²) — use when you have real and reactive power from a power analyser. (3) PF = cos(θ) — use when you have the phase angle from an oscilloscope or analyser.

What is a good power factor?

Above 0.90 is generally good. Many utilities require industrial customers to maintain PF above 0.85–0.90 or face billing surcharges. Installing power factor correction capacitors can improve PF for inductive loads like motors and transformers.