Power Factor Calculator

About the Power Factor Calculator

Calculates the power factor from real power (kW) and apparent power (kVA), or finds reactive power. A power factor near 1 means efficient use of supplied power.

How to use this calculator

1. Enter the real power value, usually measured in \(\text{watts}\) or \(\text{kW}\).
2. Enter the apparent power value, usually measured in \(\text{VA}\) or \(\text{kVA}\).
3. Check the result, which is the power factor \(PF\), a number between \(0\) and \(1\) for most AC circuits.
4. If needed, use the result to judge whether the system is operating efficiently or whether correction may help.

The formula explained

The formula \(PF = \frac{P}{S} = \cos\phi\) computes power factor by dividing real power \(P\) by apparent power \(S\). The angle \(\phi\) is the phase difference between voltage and current in an AC circuit.

• \(\text{PF}\) = power factor, the ratio of real power to apparent power
• \(P\) = real power, the useful power measured in \(\text{W}\) or \(\text{kW}\)
• \(S\) = apparent power, measured in \(\text{VA}\) or \(\text{kVA}\)
• \(\\phi\) = phase angle between voltage and current

Step by step method

1. Write down the real power \(P\) and the apparent power \(S\).
2. Divide \(P\) by \(S\) to find \(PF\).
3. If the problem gives a phase angle, you can also check your result with \(PF = \cos\phi\).

Worked example

Problem. A circuit has real power \(P = 480\text{ W}\) and apparent power \(S = 600\text{ VA}\). Find the power factor.

1. Use the formula \(PF = \frac{P}{S}\).
2. Substitute the values, \(PF = \frac{480}{600}\).
3. Compute the ratio, \(PF = 0.8\).

Tips and common mistakes

• Make sure the units match, for example \(\text{W}\) with \(\text{VA}\) or \(\text{kW}\) with \(\text{kVA}\).
• Power factor should not be greater than \(1\) when using real power divided by apparent power. If you get a value above \(1\), check your inputs.

Frequently asked questions