Power Factor Calculator

Find the power factor of an AC load, or the kVAR you need to raise it. Type kW, kVA, kVAR, or volts and amps.

Real power

The watts or kilowatts the load uses.

Apparent power

In volt-amps. A kVA is 1,000 VA.

How to calculate the power factor

In an AC circuit, the voltage times the current is the apparent power in volt-amps (VA or kVA). Only part of it does useful work. That part is the real power in watts (W or kW). The rest is the reactive power in VAR (or kVAR). The power factor (PF) is the ratio of real power to apparent power, so it is a number above 0 and up to 1.

You want	Formula
Power factor from kW and kVA	PF = kW ÷ kVA
Power factor from kW and kVAR	PF = kW ÷ √(kW² + kVAR²)
Apparent power, single-phase	kVA = V × A ÷ 1,000
Apparent power, three-phase	kVA = √3 × V × A ÷ 1,000
Reactive power	kVAR = √(kVA² − kW²)
Phase angle	φ = arccos(PF)

In the three-phase row, V is the line-to-line voltage. The power factor equals the cosine of the phase angle, and the reactive power is the square root of the apparent power squared minus the real power squared. We compared these formulas in October 2026 with an informational calculator site and with a Fluke article on power factor. The apparent power from amps and volts is also what the kVA calculator gives, and to find the current for a wattage use the watts to amps calculator.

Example 1: from kW and kVA

A load uses 100 kW and the apparent power is 125 kVA. In the calculator, use the "From kW and kVA" tab.

Step	Operation	Result
Power factor	100 ÷ 125	0.8
Reactive power	√(125² − 100²)	75 kVAR
Phase angle	arccos(0.8)	36.87°

Example 2: raise the power factor from 0.8 to 0.95

The same 100 kW load. To find the reactive power to cancel, choose "Correct the power factor", keep 100 kW and type 0.8 as the present power factor and 0.95 as the target.

Step	Operation	Result
Apparent power before	100 ÷ 0.8	125 kVA
Reactive power before	√(125² − 100²)	75 kVAR
Apparent power after	100 ÷ 0.95	105.26 kVA
Reactive power after	√(105.26² − 100²)	32.87 kVAR
Reactive power to cancel	75 − 32.87	42.13 kVAR
Apparent power drops by	125 − 105.26	19.74 kVA (15.79%)

At the same voltage the current is proportional to the apparent power, so it falls by the same 15.79%. The new current is 0.8 ÷ 0.95 = 84.21% of the old one. The kVAR is what a capacitor supplier asks for. The calculator does not choose the capacitors.

kVAR needed per kW of load

Multiply the real power in kW by the number in the table to get the kVAR to cancel. For example, raising 100 kW from 0.8 to 0.95 is 100 × 0.421 = 42.1 kVAR, the same as Example 2.

Present PF	To 0.90	To 0.95	To 1.00
0.70	0.536	0.692	1.020
0.75	0.398	0.553	0.882
0.80	0.266	0.421	0.750
0.85	0.135	0.291	0.620
0.90	—	0.156	0.484

What a lower power factor means for 100 kW

For a fixed 100 kW at a fixed voltage, a lower power factor needs more apparent power and more current. The extra current is 1 ÷ PF − 1.

Power factor	Phase angle	Apparent power	Reactive power	More current than at PF 1
1	0.0°	100.00 kVA	0.00 kVAR	0%
0.95	18.2°	105.26 kVA	32.87 kVAR	5.3%
0.9	25.8°	111.11 kVA	48.43 kVAR	11.1%
0.85	31.8°	117.65 kVA	61.97 kVAR	17.6%
0.8	36.9°	125.00 kVA	75.00 kVAR	25.0%
0.7	45.6°	142.86 kVA	102.02 kVAR	42.9%

Where to find the numbers

Use the real power, the voltage and the current from the nameplate or data sheet of the equipment, or from your own measurements. If you only have volts and amps, the "From volts and amps" tab also needs the real power, because voltage and current alone do not give it. This page does not suggest typical power factors for motors, lighting or other equipment.

What this calculator does not do

It works out the power factor or the reactive power to cancel for a balanced load, from the numbers you type. It does not choose capacitors or any other equipment and it does not apply any margin. For circuit protection, see the breaker size calculator. The electrical code adopted where you live and the equipment makers' instructions set the final rules, and a licensed electrician should confirm them. Nothing you type leaves your browser.

Frequently asked questions

How do you calculate the power factor?

Divide the real power in kilowatts by the apparent power in kVA: PF = kW ÷ kVA. If you only know volts, amps and kilowatts, first find the apparent power. For single-phase, kVA = volts × amps ÷ 1,000. For three-phase, kVA = √3 × line-to-line volts × amps ÷ 1,000. For example, 12 kW with 15 kVA gives 12 ÷ 15 = 0.8.

What is a 0.95 power factor?

It means the real power is 95% of the apparent power. For a load of 100 kW, a power factor of 0.95 means an apparent power of 100 ÷ 0.95 = 105.26 kVA and a reactive power of 32.87 kVAR. The phase angle is the arccos of 0.95, about 18.19 degrees.

What is the ideal power factor for a house?

The highest possible value is 1, where all the apparent power is real power. This page does not give a target for homes, because we did not find a source for one. A licensed electrician or your electric utility can tell you whether the power factor matters for your service.

How do I calculate the power factor from kW?

You need a second number besides the kilowatts. With the apparent power in kVA, divide: PF = kW ÷ kVA. With the reactive power in kVAR, use PF = kW ÷ √(kW² + kVAR²). With volts and amps, find the kVA first. The calculator has a tab for each case.

How do I correct a low power factor?

One way is to add capacitors. The kVAR to cancel is the reactive power before minus the reactive power at the target, where Q = √(S² − P²) and S = P ÷ PF. Raising 100 kW from a power factor of 0.8 to 0.95 takes 75 − 32.87 = 42.13 kVAR. The "Correct the power factor" tab does this. Choosing and installing the capacitors is a job for a supplier and a licensed electrician.

Why does a low power factor matter?

For the same real power and voltage, a lower power factor means more current, in proportion to 1 ÷ PF. At a power factor of 0.8 the current is 25% higher than at 1. A Fluke article lists higher current and heat damage to insulation and other circuit components among the consequences of a poor power factor.

Can I use this to size a capacitor bank or choose equipment?

No. The result is the reactive power to cancel from the numbers you type. The size and type of capacitor bank, the voltage rating and the protection depend on more than that, and the electrical code adopted where you live adds requirements this calculator does not apply. Ask a supplier and a licensed electrician.