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Power Factor Calculator

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Find the power factor of an AC electrical system from real power (kW) and apparent power (kVA) - a key efficiency measure for motors, HVAC equipment, and industrial electrical systems.

Power Factor Calculator

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Power factor
0.833
As percentage
83.3%
Reactive power
2.0 kVAR
Power factor is always between 0 and 1 (or 0-100%).

The formula

Power factor = Real power (kW) / Apparent power (kVA) Reactive power (kVAR) = sqrt(Apparent power^2 - Real power^2)
Example

A system drawing 3.6 kVA apparent power while doing 3.0 kW of real, useful work: power factor = 3.0 / 3.6 ≈ 0.833 (83.3%), with about 2.0 kVAR of reactive power not doing useful work.

Step-by-step guide

  1. Find your real power (kW) - this is the actual useful work being done, typically from equipment nameplate data or a power meter.
  2. Find your apparent power (kVA) - the total power the system draws, including both useful and reactive components.
  3. Read the power factor - closer to 1.0 (or 100%) means more efficient use of the electrical supply.

Why power factor matters

Real power does actual useful work (spinning a motor, heating an element), while reactive power is drawn by inductive loads (motors, transformers, fluorescent ballasts) to establish magnetic fields but doesn't do useful work directly. A low power factor means the system draws more total current from the supply than the real power alone would suggest, which increases losses in wiring and transformers and often leads utilities to charge industrial and commercial customers a penalty for poor power factor.

Common mistakes

Confusing kW (real power) with kVA (apparent power) on equipment nameplates - generators and UPS systems are often rated in kVA, while the actual usable load capacity in kW depends on the power factor.
Assuming a power factor issue only matters for large industrial sites - many utilities apply power factor penalties to commercial customers with poor power factor, not just heavy industry.

Frequently asked questions

What's considered a "good" power factor?

0.95 or higher is commonly considered good, and many utilities set penalty thresholds somewhere in that range - check your specific utility's tariff for their exact requirement.

How can power factor be improved?

Power factor correction capacitors are commonly installed to offset the reactive power drawn by inductive loads like motors, bringing the overall power factor closer to 1.0 - this is typically an electrical engineering decision made at a facility level, not a household one.

Does a residential home need to worry about power factor?

Most residential customers aren't billed based on power factor and don't need to actively manage it - this is primarily relevant for commercial and industrial facilities with large motor loads.

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