kW to kVA Calculator for Generator & UPS Sizing

To convert kW to kVA, divide the real power in kilowatts by the power factor. Apparent power in kilovolt-amps equals real power in kilowatts divided by power factor, so kVA = kW ÷ PF. The same formula works for single-phase and three-phase, because the phase is already accounted for in the power figures.

kW is the real power a load actually uses; kVA is the total, or apparent, power the source must supply to deliver it. Because the power factor is never more than 1, the kVA is always at least as large as the kW. This is the conversion you use to size a generator, transformer, or UPS from a known kW load, since that equipment is rated in kVA. To go the other way, the kVA to kW calculator multiplies by the power factor and explains the kW-versus-kVA difference in full.

kW to kVA Formula

There is no voltage, phase, or three-phase factor in this conversion. Those all sit inside the power figures already, so a three-phase kW converts to kVA exactly the same way a single-phase kW does: divide by the power factor. A power factor of 1 (a purely resistive load) makes kVA equal to kW; any lower power factor makes the kVA larger.

How to Use the kW to kVA Calculator

1. Enter the real power in kW. This is the working load, or the kW rating on an equipment nameplate.
2. Enter the power factor. Use the load's actual value if you know it, 0.8 for a typical generator or motor load, or 1 for a purely resistive load like a heater.
3. Read the apparent power in kVA. That is the minimum kVA the transformer, generator, or UPS must be rated for.

kW to kVA Worked Examples

Example 1: Sizing a Generator for an 80 kW Load

A building has an 80 kW standby load, and generator sets are rated at a 0.8 power factor:

kVA = 80 ÷ 0.8 = 100 kVA

So an 80 kW load needs a 100 kVA generator. In practice you would round up to the next standard size and add margin for motor starting and future growth.

Example 2: 40 kW Load at 0.8 Power Factor

A 40 kW load at a 0.8 power factor requires:

kVA = 40 ÷ 0.8 = 50 kVA

A 50 kVA transformer or generator covers this load exactly at 0.8 power factor.

Example 3: 100 kW Data-Center Load at 0.9 Power Factor

A 100 kW IT load running at a 0.9 power factor needs:

kVA = 100 ÷ 0.9 = 111.1 kVA

The better power factor keeps the required kVA lower than it would be at 0.8, where the same 100 kW would need 125 kVA.

Example 4: 10 kW Resistive Load (Power Factor 1.0)

A purely resistive load, such as an electric heater bank, runs at a power factor of 1:

kVA = 10 ÷ 1.0 = 10 kVA

Here kVA and kW are equal, because there is no reactive power to supply.

kW to kVA Conversion Chart

This chart shows the apparent power in kVA that common kW loads require at three power factors. The required kVA falls as the power factor improves, and equals the kW only at a power factor of 1.

Sizing a Generator, Transformer, or UPS From a kW Load

The most common reason to convert kW to kVA is to size equipment. Generators, transformers, and UPS units are rated in kVA, but loads are usually described in kW, so kVA = kW ÷ PF tells you the minimum rating the equipment needs. An 80 kW load at a 0.8 power factor needs at least 100 kVA of apparent power.

That figure is a minimum, not a final answer. Round it up to the next standard kVA rating (15, 30, 45, 75, 112.5, 150, 225, 300, 500 kVA, and so on), and add headroom for motor inrush, non-linear loads, and future growth. Standby generator sets are rated at a 0.8 power factor by convention (ISO 8528, the generator-set standard), which is why their kVA rating is 1.25 times their kW rating. The kVA you calculate also sets the current the equipment must carry; convert it with the kVA to amps calculator to size the breaker and cable.

Why the Phase Doesn't Change kW to kVA

Converting kW to kVA is the same for single-phase and three-phase systems: kVA = kW ÷ PF either way. People often look for a separate three-phase formula with a three-phase factor in it, but that factor belongs to the current conversions, not this one. The three-phase factor and the voltage are already built into the power figures, so once you have the kW there is nothing phase-specific left to do. A 50 kW three-phase load at 0.8 power factor is 62.5 kVA, the same as a 50 kW single-phase load.

Why kVA Is Always Bigger Than kW

Apparent power in kVA is never smaller than real power in kW, because the power factor is at most 1. When the power factor is 1, all the apparent power does real work and kVA equals kW. When it is less than 1, the source has to supply extra current for reactive power that does no net work, so the kVA exceeds the kW. The lower the power factor, the bigger the gap. When a nameplate doesn't state the power factor, use these typical values.

Apparent, real, and reactive power are defined in IEEE Std 1459, the IEEE standard for electric power quantities.

kW vs kVA in Brief

kW is real power, the part that does useful work; kVA is apparent power, the total the source must supply. They differ by the power factor and are equal only when it is 1. You size cables, breakers, transformers, and generators in kVA because they are limited by current, and you count energy and motor output in kW. For the full comparison of when to use each, see the kVA to kW calculator, and for what apparent power means see the amps to kVA calculator.

Common Mistakes When Converting kW to kVA

• Assuming kW equals kVA. They are equal only at a power factor of 1; an 80 kW load needs 100 kVA of equipment at a 0.8 power factor, not 80 kVA.
• Adding a three-phase factor. kVA = kW ÷ PF is the same for any phase; the three-phase factor belongs to the current conversions.
• Sizing to the exact kVA. The result is a minimum; round up to a standard rating and add margin for inrush and growth.
• Using the wrong power factor. The kVA scales inversely with it, so a guessed power factor gives a guessed size. Use the load's actual value where you can.
• Dividing by the power factor twice. If a figure is already in kVA, it does not need converting again.

Disclaimer: This calculator converts real power to apparent power at the power factor you enter, giving a minimum kVA. Equipment selection also depends on inrush, non-linear loads, ambient conditions, and margin. Always verify against manufacturer data and your local electrical code, and consult a licensed electrician or professional engineer for equipment sizing and installation. Generator and UPS ratings follow standards such as ISO 8528; confirm the assumed power factor on any nameplate.