About the Power Factor Calculator
Power Factor Calculator works with the three kinds of power in an AC circuit: real power in kilowatts (kW), apparent power in kilovolt-amperes (kVA) and reactive power in kilovolt-amperes reactive (kVAr). Fill in any two of kW, kVA and the power factor to get the rest, with the phase angle. Or enter voltage, current and power factor for a single-phase or three-phase supply to get the apparent and real power. A correction mode tells you how big a capacitor bank (in kVAr) is needed to raise a low power factor to a target such as 0.95, and shows the current before and after. It is meant for planning and for learning. Choosing and installing capacitors for real equipment should be done by a qualified electrician or engineer, with attention to harmonics and the local rules.
Updated September 2026
How to use the Power Factor Calculator
- 1Choose Find PF or kW/kVA, From volts and amps, or Correction.
- 2For the first mode, fill in any two of real power, apparent power and power factor.
- 3For volts and amps, pick single-phase or three-phase and enter voltage, current and power factor.
- 4For correction, enter the load in kW, the present and target power factor, and the voltage.
- 5Read the results: power factor, kVA, kVAr, the capacitor size and the current before and after.
Why power factor matters
A supply must be able to deliver the full current, whether or not that current does useful work. A factory with a power factor of 0.7 needs about 43 percent more current than one with a power factor of 1 for the same real power. This means bigger cables, transformers and switchgear, more heat losses in the wires and, often, a penalty charge from the electricity company.
Improving the power factor cuts the current, frees capacity on existing wiring and lowers losses. In many industrial sites, a correction capacitor bank pays for itself within a year or two.
The power triangle
- Real power (kW) is the base of the triangle: the power that does useful work.
- Reactive power (kVAr) is the height: it builds magnetic fields in motors and transformers.
- Apparent power (kVA) is the hypotenuse: what the supply must deliver.
- Power factor is the cosine of the angle between real and apparent power.
- Correction with capacitors shortens the reactive side and so lowers kVA.
Example of correction
A workshop draws 100 kW at a power factor of 0.8 from a 400 V three-phase supply. The current is 100,000 ÷ (1.732 × 400 × 0.8), about 180 A. To raise the power factor to 0.95 the capacitor bank needs 100 × (tan 36.87° − tan 18.19°) = 100 × (0.75 − 0.329), about 42 kVAr. The current then falls to about 152 A, which is 15 percent less.
Do not correct beyond a power factor of 1 or to a leading value, and ask an electrician about harmonics when many variable-speed drives are present, since capacitors can resonate with them.
Tips and related tools
Use the line-to-line voltage for three-phase supplies. For converting between kVA, kW and amps in generator and UPS sizing, kVA to kW Calculator gives a shortcut, and Watts, Amps and Volts Calculator covers direct conversions. Voltage Drop Calculator shows how the lower current from a better power factor reduces the loss in a cable.
Ohm's Law Calculator solves the basic relationships, and Electricity Cost Calculator shows what a load costs to run. Always follow local electrical rules, and have work on the mains done by a qualified person.
Features
- Power factor from kW and kVA
- kW and kVA from each other and the power factor
- Reactive power and phase angle
- Single-phase and three-phase apparent power from volts and amps
- Capacitor size (kVAr) for power factor correction
- Current before and after correction
- Runs in your browser
Frequently asked questions
What is power factor?
Power factor is the ratio of real power, which does useful work, to apparent power, which is the voltage times the current. It is a number from 0 to 1. A value of 1 means all the power drawn does useful work, while a lower value means part of the current is going to and fro without doing work, as with motors and transformers.
How do I calculate power factor?
Divide the real power in kW by the apparent power in kVA. A load that uses 80 kW and is rated at 100 kVA has a power factor of 0.8. Enter any two of the three values in the tool and the third is calculated.
What is a good power factor?
Close to 1 is ideal. Many utilities want a power factor of 0.9 or 0.95 or higher, and charge extra when a business's power factor is lower, since the extra current needs bigger cables and transformers. Resistive loads such as heaters have a power factor near 1, and lightly loaded motors can be as low as 0.3 to 0.5.
How do I correct a low power factor?
Most low power factors come from inductive loads such as motors, and they are corrected by adding capacitors that supply the reactive power locally. The size needed is kW × (tan of the present angle − tan of the target angle). The correction mode calculates this for you.
What is the difference between kW, kVA and kVAr?
kW is the real power that does work, kVA is the total apparent power that the supply must provide, and kVAr is the reactive power that moves back and forth. They form a right triangle where kVA² = kW² + kVAr², which is why kVA is never smaller than kW.
Why does the three-phase supply use the square root of 3?
In a three-phase system, the line-to-line voltage times the current times √3 gives the total apparent power. Use the line-to-line voltage, such as 400 V, in the tool, and choose Three-phase.