Power Factor Calculator
Real against apparent power, and the current it costs.
Work out Power Factor. Real against apparent power, and the current it costs. Answers in more than one unit, because SI is not always the legible one.
Optional — gives the current drawn.
Power factor
0.8
36.87° out of phase · 600 VAR
Power factor is real power over apparent power — the share of what the supply delivers that actually does work. At 0.8 the remaining current still flows and still heats the cables, it simply accomplishes nothing, which is why industrial tariffs charge for it. The three powers form a right triangle: 800 W and 600 VAR give 1,000 VA as the hypotenuse.
How the Power Factor Calculator works
Power factor is real power over apparent power — the share of what the supply delivers that actually does work. The rest still flows and still heats the cables, it simply accomplishes nothing, which is why industrial tariffs charge for it.
Also known as: kva to kw calculator · reactive power calculator · power factor correction calculator · power factor formula
Real, apparent and reactive
Real power in watts does work. Apparent power in volt-amps is what the supply must deliver. Reactive power in VAR is the difference — current that flows out and back without accomplishing anything.
The three form a right triangle: 800 W of real power and 600 VAR of reactive power give 1,000 VA apparent, by Pythagoras.
Why it is billed
Reactive current still flows through every cable, transformer and switch between the generator and the load. It still heats them, and they still have to be sized for it.
So a factory drawing 800 kW at a power factor of 0.8 imposes the same infrastructure cost as one drawing 1,000 kW at unity — while paying for less energy. Industrial tariffs charge for power factor to close that gap.
The usual fix is a capacitor bank. Motors and fluorescent lighting are inductive and lag the voltage; capacitors lead it, and the two cancel. Correcting to above 0.95 is the common target.
Frequently asked questions
What is power factor?
The ratio of real power in watts to apparent power in volt-amps. 800 W drawn as 1,000 VA is a power factor of 0.8.
Why does a poor power factor cost money?
Because the supply must carry the full apparent current, sizing cables and transformers for power that does no work. Industrial tariffs bill for it directly.
What is reactive power?
The component that flows back and forth without doing work, measured in VAR. The three powers form a right triangle — 800 W and 600 VAR give 1,000 VA.
What is a good power factor?
Above 0.95 is generally considered good, and unity is ideal. Motors and fluorescent lighting are common causes of poor power factor, which capacitor banks are used to correct.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/power-factor-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Power Factor Calculator"></iframe>The only condition is that the credit line stays visible. It sits inside the frame, so you do not have to do anything to keep it.
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