Calculation reviewed: 4 October 2026 · Engineering Desk Tools
How to use the Power factor correction calculator
Find the capacitor kVAR needed to raise power factor and see the reduction in apparent power and current. Start with measurements or documented values for the equipment and reporting period you actually want to assess. The calculator does not fill in a typical installation for you. Its blank fields help keep a demonstration value from being mistaken for your own operating data.
Choose the required options, enter the values in the labelled units and select Calculate. If a field is rejected, check its range and unit before changing it. The result is accompanied by the equation and assumptions so you can decide whether it answers your engineering question.
Inputs and measurement basis
- Active power (kW). Average active power over the billing or study period, in kW. The value must be greater than zero.
- Existing power factor (decimal, up to 1). Existing average power factor, from a meter or your bill, as a decimal. The allowed maximum is 1. The value must be greater than zero.
- Target power factor (decimal, up to 1). The value you want to reach, as a decimal; commonly 0.95 to 0.98. It must be above the existing value. The allowed maximum is 1. The value must be greater than zero.
Record the measurement source and operating condition. Retain unrounded values for verification.
Method and interpretation
Reactive power is the part of apparent power that does no useful work. Correcting power factor means supplying some of it locally, which lowers apparent power and line current for the same kW. The kVAR needed equals kW multiplied by the difference between the tangents of the two power-factor angles. The correction does not change the kW consumed.
kVAR = kW × (tan φ1 − tan φ2), where tan φ = √(1 / PF² − 1). Apparent power = kW / PF.
Use the average active power and power factor over the period that matters, such as the billing interval. Capacitor kVAR rating is specified at rated voltage and changes with the square of the applied voltage. Harmonics, resonance, switching steps and detuning reactors need separate engineering review. Avoid over-correction, which can leave a leading power factor.
Worked example
This example does not populate the form. Enter your own installation data.
Calculated result: 42.1316 kVAR of correction. Select a standard capacitor rating near the calculated value and confirm harmonics, voltage and switching with the supplier.
Check the arithmetic independently using the displayed equation. Retain intermediate precision and compare the final value with your equipment documentation.
Quick-reference table
These are illustrative values, not certified ratings or manufacturer data. Use the form for your own conditions.
Common mistakes
Using peak instead of average kW; sizing capacitors at the wrong voltage; ignoring harmonics, which can overload capacitors; correcting past unity so the load looks leading; assuming correction at the incomer reduces current inside the plant. Before relying on the output, check the decimal format, unit scale and source of each value. Recheck unusual results against the formula.
Frequently asked questions
Are the example values used automatically?
No. Inputs remain blank when the tool opens or when you clear them. The worked example and table are reading material below the calculator. Enter the actual values you want to check each time, and label saved reports so their context is not lost.
What does the result mean?
The result is the capacitor kVAR needed to raise the power factor from the existing to the target value, with the matching drop in apparent power and current. Choose a standard step size and confirm harmonics before purchase.
Can I use a zero or a negative value?
The allowed range follows the meaning of each input. A divisor needs a positive value; other fields may allow zero. Check the form labels and error message rather than forcing an invalid value. A rejected input must be corrected before a result can be shown.
Is this a final design or equipment approval?
No. Use the average active power and power factor over the period that matters, such as the billing interval. Capacitor kVAR rating is specified at rated voltage and changes with the square of the applied voltage. Harmonics, resonance, switching steps and detuning reactors need separate engineering review. Avoid over-correction, which can leave a leading power factor. Use the calculation as support for a checked decision, and review equipment documentation and applicable requirements before changing an installation or operating setting.
How can I save or share a calculation?
Calculate first, then use Copy result or Print report. Some maintenance tools also provide a CSV summary. Reports contain your own entered data, so review them before sharing. You can share the public page URL without including plant records or confidential measurements.
How do I report an unexpected result?
Use the Contact page and include the tool URL, input values, units, expected output and the reference you used. Explain the measurement basis. Exclude confidential information.
Related tools and records
Use related calculations with consistent units, periods and equipment scope.
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