kVA to kW Calculator

Read a kVA nameplate as kilowatts: the real power a UPS, generator or transformer can carry at a given power factor.

Inputs

Result

Enter the kVA rating to see the real power in kW.

Related tools

How the calculation works

Real power in kW is apparent power multiplied by the power factor (PF):

kW = kVA × PF
kVAR = √(kVA² − kW²), the reactive power the unit also supplies

The kVAR figure assumes sinusoidal current. With nonlinear loads such as server power supplies, part of the difference between kVA and kW is harmonic distortion rather than reactive power, so the result card labels it “if sinusoidal”. The kW result does not depend on that assumption.

A kVA rating is the current a UPS, generator or transformer can deliver, expressed at its rated voltage. How much useful (real) power that allows depends on the power factor. Enter the PF from the nameplate or data sheet to read the unit’s kW rating, or your load’s PF to see how much real power it can draw before reaching the kVA limit.

The default PF is 0.9, a common planning value for IT loads; a UPS data sheet states its own output power factor. Use 0.8 for generator sets rated to the ISO 8528-1 convention. Voltage and phase do not enter this conversion.

Worked example

A 500 kVA standby generator is rated at a power factor of 0.8:

kW = 500 × 0.8 = 400 kW
kVAR = √(500² − 400²) = 300 kVAR

A 100 kVA UPS has an output power factor of 0.9:

kW = 100 × 0.9 = 90 kW
kVAR = √(100² − 90²) = 43.59 kVAR

So the UPS carries up to 90 kW of IT load. The load also has to stay within 100 kVA, which matters only if its power factor is below 0.9.

Frequently Asked Questions

How many kW is a 500 kVA generator?

Generator sets are commonly rated at a power factor of 0.8, the convention in ISO 8528-1, so 500 kVA × 0.8 = 400 kW. The data sheet usually lists both figures; if it gives a kW rating, use that.

Why do generator and UPS ratings use different power factors?

They describe different machines. A generator set's kW rating commonly assumes a power factor of 0.8, following ISO 8528-1, unless its data sheet says otherwise. A UPS rating describes its inverter output, and each model states its own power factor; some recent models are rated at 1.0, meaning kW equals kVA.

What if my load's power factor is lower than the rating's?

Then the kVA limit is reached first. A 100 kVA unit rated at 0.9 carries 90 kW, but a load with a power factor of 0.8 reaches 100 kVA at only 80 kW.

Does a generator's kW change between standby and prime ratings?

Yes. ISO 8528-1 defines several ratings, and a set's emergency standby rating is higher than its prime or continuous rating. Compare quotes at the same rating class, and use the one that matches how the generator will run.