kW to kVA Calculator

Find the apparent power in kVA that a UPS, generator or transformer must supply to carry a load in kilowatts.

Inputs

Result

Enter the load in kW to see the apparent power in kVA.

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How the calculation works

Apparent power in kVA is real power divided by the power factor (PF):

kVA = kW ÷ PF
kVAR = √(kVA² − kW²), the reactive power

kW, kVA and kVAR form a right triangle: kW along one side, kVAR along the other, kVA as the long side. The power factor is kW ÷ kVA. At a PF of 1.0, kVA equals kW and there is no reactive power. The triangle holds exactly for sinusoidal current; with nonlinear loads such as switch-mode power supplies, part of the gap between kVA and kW is harmonic distortion rather than reactive power, so the calculator labels kVAR “if sinusoidal”.

The default PF here is 0.9, a common planning value for IT loads with power-factor-corrected supplies; at 1.0 the conversion would change nothing. If you have a measured PF from the UPS or PDU, use it. The presets include 0.8 because generator sets are commonly rated at that power factor.

Voltage and phase play no part in this conversion. To turn the kVA into current, use the kVA to amps calculator.

Worked example

An IT room carries 40 kW of load at a power factor of 0.9, and you are checking a UPS for it:

kVA = 40 ÷ 0.9 = 44.44 kVA
kVAR = √(44.44² − 40²) = 19.37 kVAR

A UPS rated 50 kVA / 45 kW (output power factor 0.9) carries this load on both counts: 40 kW is under 45 kW, and 44.44 kVA is under 50 kVA. Planning for redundancy and growth comes on top of that.

If the load’s power factor were 1.0, the same 40 kW would need only 40 kVA.

Frequently Asked Questions

Is 1 kW the same as 1 kVA?

Only at a power factor of 1.0. kW is real power, the work the equipment does; kVA is apparent power, volts × amps. At a power factor of 0.9, a 40 kW load needs 44.44 kVA.

Why are UPS systems rated in both kVA and kW?

A UPS has two limits: the current its output can deliver, expressed as kVA, and the real power its inverter can supply, in kW. The ratio kW ÷ kVA is its rated output power factor. Check the load against both: its kW must fit under the kW rating and its kVA under the kVA rating.

What is kVAR?

Reactive power: the part of apparent power that flows back and forth between source and load without doing work. With sinusoidal current, kVA² = kW² + kVAR², so 40 kW at a power factor of 0.9 is 44.44 kVA with 19.37 kVAR. Server and UPS power supplies also draw distorted (harmonic) current, so for them the figure overstates the true reactive power somewhat; the kVA and kW results are unaffected.

Do voltage and phase matter for kW to kVA?

No. kVA = kW ÷ power factor at any voltage, single-phase or three-phase. Voltage only matters when you go on to current; the kVA to amps calculator does that step.