Power Factor Calculator - kW, kVA and Phase Angle

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Ohm's law and standard electrical engineering formulas

Power factor is the ratio of real power to apparent power. PF = kW / kVA. A PF of 1 is tidy. Motors, transformers and old lighting usually pull it lower, which means more current for the same useful work.

Formula at a glance

  • PF = kW / kVA
  • PF = W / VA
  • PF = cos(phase angle)

Field note: Do not guess PF if a nameplate or power meter gives it. A wrong PF makes every downstream amp, kVA and wire-size estimate worse.

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Power Factor Calculator

Calculate power factor (PF)

W
VA
Result
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Formula

PFPF = P ÷ S
AlsoPF = cos(θ)

Power Factor ranges from 0 to 1

Typical Power Factors

Load Type PF
Resistive (heaters) 1.0
Fluorescent lights 0.9-0.95
Induction motors 0.7-0.85
Unloaded motors 0.2-0.3

Related

kW to kVAkVA to kW

How to use the Power Factor Calculator

Use this as a fast electrical check, then compare the result with the nameplate, measured voltage and power factor. The formula is clean. Real panels, motors and UPS loads usually have one extra wrinkle.

Worked example

Example: a load using 8 kW from 10 kVA has PF = 0.8. The supply carries 10 kVA even though only 8 kW becomes useful power.

Practical checks before you trust the number

  • Loaded induction motors usually have better PF than lightly loaded motors.
  • Capacitor banks can improve lagging PF, but overcorrection causes its own problems.
  • Utilities may penalize poor PF on commercial accounts.

Common mistake

Do not guess PF if a nameplate or power meter gives it. A wrong PF makes every downstream amp, kVA and wire-size estimate worse.

Sources and references

Related calculators

Frequently Asked Questions

PF = real power (W) ÷ apparent power (VA). Or PF = cos(θ), where θ is the phase angle between voltage and current. Example: 800 W real, 1000 VA apparent → PF = 0.8. PF is unitless and ranges from 0 to 1.

PF = kW ÷ kVA. Example: 8 kW real, 10 kVA apparent → PF = 0.8. This is the most common way to compute PF from meter readings on a panel. Most digital meters now display PF directly, but knowing the formula lets you sanity-check.

PF = W ÷ VA = real power ÷ apparent power. Example: 1500 W ÷ 2000 VA = 0.75. Use this to characterize loads when both watts and VA are known. Key for sizing UPS, generators, and PF correction capacitors.

Modern energy-efficient three-phase induction motors run at PF 0.85 to 0.92 at full load. Single-phase motors are lower, around 0.7 to 0.85. PF drops sharply at part-load — a motor running at 30% load might have PF 0.5 or lower. Aim for 0.95 plus on facility-wide PF after correction; many utilities penalize below 0.9.

Because for the same real power (kW), low PF means higher apparent current. I = kW ÷ (V × PF), so PF in the denominator inflates current as PF drops. Example: 1 kW at PF 1 on 230 V → 4.35 A; same 1 kW at PF 0.5 → 8.7 A. Cables and breakers carry the higher current and waste more energy as I²R losses.

Add capacitor banks in parallel with inductive loads. Capacitors generate leading reactive power that cancels the lagging reactive power of motors and ballasts. Size the capacitor in kVAR using kVAR = kW × (tan(θ_old) − tan(θ_new)). Most facilities install automatic PF correction panels that switch capacitor stages based on real-time PF measurement.

Yes. Generators are rated at a specific PF (usually 0.8 lagging). If your actual load PF is much lower, the generator can supply less kW than its rating suggests. Calculate actual kW from kVA × measured PF and compare. Overloaded generators stall and trip — undersizing on PF is a common mistake.