Power Factor Calculator
Calculate power factor, phase angle, and reactive power from real and apparent power.
How it works
- 1Enter the real power in watts (W) — the usable power consumed.
- 2Enter the apparent power in volt-amperes (VA) — the total power drawn.
- 3The calculator divides real by apparent power for the power factor, then derives phase angle and reactive power.
Use cases
- Assessing whether motors or HVAC systems need capacitor correction.
- Checking a generator or UPS is not overloaded by reactive loads.
- Estimating reactive power (VAR) when sizing correction capacitors.
Frequently asked questions
What is a good power factor?
A power factor of 0.95 or above is excellent; 0.85–0.95 is acceptable. Below 0.85, utilities often apply penalties and correction is worthwhile.
How is power factor calculated?
Power factor = real power (W) ÷ apparent power (VA) = cos φ. For example, 800 W ÷ 1000 VA = 0.8, giving φ ≈ 36.87° and 600 VAR.
Why does reactive power matter?
Reactive power (VAR) does no useful work but still flows through cables and transformers, causing losses and reducing capacity. Correction lowers bills.
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