Power Factor Calculator

Power Factor in AC Circuits

Power factor compares real power that performs work to apparent power supplied to the circuit. A power factor of 1.0 means all supplied power is useful. Lower values indicate reactive power circulating without doing work.

Formulas

$$ PF = \frac{P}{S} = \cos \phi $$

$P$ is real power in watts, $S$ is apparent power in volt-amperes, and $\phi$ is the phase angle between voltage and current. Reactive power is:

$$ Q = \sqrt{S^2 - P^2} $$

The power triangle relates real, reactive, and apparent power through the Pythagorean theorem.

Practical Notes

Inductive loads such as motors reduce power factor. Utilities may charge industrial customers for poor power factor because it increases current demand on the grid. Capacitor banks are often added to improve power factor.

Frequently Asked Questions

What is a good power factor?

Values above 0.95 are generally considered good. Many facilities target 0.90 or higher to avoid utility penalties.

What does a power factor of 0.75 mean?

Only 75% of supplied apparent power does real work. The remaining 25% is reactive power that oscillates in the circuit.

Does power factor have units?

No. Power factor is a dimensionless ratio between 0 and 1, often shown as a decimal or percentage.

How is power factor related to phase angle?

Power factor equals the cosine of the phase angle between voltage and current. Zero phase angle gives unity power factor.

Can real power exceed apparent power?

No. Real power is always less than or equal to apparent power, so power factor cannot exceed 1.

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Power Factor in AC Circuits

Formulas

Practical Notes

Frequently Asked Questions

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