Power Converter (kW / kVA / VA)
Enter what you know — apparent power in kVA, real power in kW, or volts and amps — and the converter fills in the rest, including the current the load draws at your supply voltage and the reactive power the wiring still has to carry.
Real power in kW is what does the work and what a meter bills; apparent power in kVA is what the cables, breakers and transformer windings have to carry. The gap between them is reactive power (kvar), which shuttles back and forth without doing useful work. Utilities usually want a power factor of 0.90 or better and may charge for poor power factor, so a load that measures badly on this page is worth correcting with capacitors. Power factor is a property of the load, not of the supply, and it gets worse when motors run lightly loaded.
Formula and calculation
Worked example
A 100 kVA load at a power factor of 0.9 draws 90 kW of real power and 43.59 kvar of reactive power, while the apparent power stays at 100 kVA. On a single-phase 240 V supply that is a current of 416.67 A — compare it with the breaker feeding the load.
Why generators and transformers are rated in kVA
A 100 kW generator and a 100 kVA generator are not the same machine. The winding has to carry a certain current and lose a certain amount of heat regardless of whether that current is in step with the voltage, so the real limit is apparent power — which is why generators, transformers and UPS units come with a kVA rating and often a separate kW rating at a stated power factor, such as 80 kW at 0.8 PF.
That has a practical consequence: the same kVA delivers less useful power when the power factor is poor. Run a 100 kVA generator at 0.8 and you get 80 kW of work; improving the load to 0.95 gets you 95 kW from the same machine. If a utility is charging you for reactive power, capacitors at the load are usually cheaper than a bigger supply.
What the results mean
- Real power
- The real power in kilowatts — the part of the load that does useful work and that a meter records. It is what you entered, or kVA multiplied by the power factor.
- Apparent power
- The apparent power in kilovolt-amps — voltage times current without regard to phase. Cables, breakers, transformers and generators are sized on this number, because they are limited by current, not by useful work.
- Current at 240 V single-phase
- The current the load draws at the voltage you entered: I = S ÷ (k × V), where k is 1 for a single-phase supply and √3 for a three-phase one. Compare it with the breaker rating and the conductor ampacity.
- Real power in watts
- The same real power expressed in watts, for nameplates and data sheets that use plain watts instead of kilowatts.
- Apparent power in volt-amps
- The same apparent power expressed in volt-amps, the unit small loads such as LED drivers and control transformers are usually rated in.
- Reactive power in kvar
- The reactive power in kilovolt-amps reactive — the part of the apparent power that shuttles back and forth between the supply and the magnetic fields of motors without doing work. It is what power-factor correction capacitors cancel out.
- Substituting your numbers
- The formula with your own numbers substituted, so you can check the arithmetic by hand.
Frequently asked questions
How do I convert kVA to kW?
Multiply the kVA by the power factor: 100 kVA at 0.8 PF is 80 kW. You cannot skip the power factor, because kVA counts the whole current while kW counts only the part of it that is in step with the voltage and does work.
What power factor should I use for a motor?
Use the nameplate value if you have it, otherwise about 0.85 for an induction motor at full load. Motors drop a long way at part load — a motor idling can sit near 0.2 — so a motor that measures badly here may simply be oversized for its job.
Why is kW always less than kVA?
Because the power factor is a number between 0 and 1. kW = kVA × PF, so real power can only equal apparent power when the load is purely resistive and the voltage and current cross zero at the same instant. The difference between the two is the reactive power that magnetises coils and charges capacitors.
Does the three-phase mode use line-to-line voltage?
Yes. For a balanced three-phase load the apparent power is √3 × V × I, where V is the line-to-line voltage (240 V, 400 V, 480 V) and I is the line current. On a 400 V three-phase supply a 20 A load is about 13.9 kVA, not the 8 kVA that the single-phase formula would give you.
Is this the same number a utility would bill me for?
The real power in kW, yes — that is what a watt-hour meter records, give or take the metering accuracy. Utilities with a power-factor clause also bill a penalty or a reactive charge when the power factor falls below their threshold, commonly 0.90, which is the main reason to care about the kVA and kvar rows.