kW to kVA Calculator
Convert between real power (kW) and apparent power (kVA) using power factor — the number you need to size generators, transformers and UPS units.
Generators are rated in kVA at 0.8 PF; resistive loads are near 1.0.
A generator rated 5 kVA delivers only ~4 kW of real power at 0.8 power factor.
How this conversion works
kVA = kW ÷ power factor and kW = kVA × power factor.Reactive power
kVAR = √(kVA² − kW²). Power factor is the ratio of useful (real) power to the total (apparent) power the source must supply.Real power vs apparent power
Real power (kW) is the power that does actual work; apparent power (kVA) is the total the source has to supply, including the reactive part that motors and transformers push back and forth without consuming. Power factor is the ratio between them. Generators, transformers and UPS units are rated in kVA because their limit is set by current and voltage, not by how much real work the load happens to do.
Why it matters for sizing
A generator rated 5 kVA at 0.8 power factor only delivers about 4 kW of real power. Size backup gear on kVA and you will not be caught short. See the generator sizing and inverter sizing tools for the load side.
Frequently asked questions
Divide the real power in kW by the power factor. For example, 5 kW at 0.8 power factor is 5 / 0.8 = 6.25 kVA.
Because a generator is limited by the current and voltage it can supply, which is apparent power. The real power (kW) it can deliver depends on the load power factor, usually assumed at 0.8.
1.0 is ideal (all supplied power does work). Homes and mixed loads sit around 0.85 to 0.95; large motor loads can fall to 0.7 to 0.8 unless corrected with capacitors.
It is the portion of apparent power that oscillates between source and load without doing net work, needed to sustain magnetic fields in motors and transformers. It is the vector difference between kVA and kW.
Sources & standards
Real power, apparent power and power factor are formally defined electrical-engineering terms — these references back the definitions and typical values used above.
- Electropedia (IEC 60050) — International Electrotechnical Vocabulary — International Electrotechnical Commission
Official definitions of active power, apparent power, reactive power and power factor used in the kW-to-kVA conversion. - NIST Special Publication 811 — Guide for the Use of the International System of Units (SI) — National Institute of Standards and Technology
Reference for correct SI unit notation and conversion practice applied to kW, kVA and kVAR figures. - ANSI/NEMA MG 1 — Motors and Generators — National Electrical Manufacturers Association
Standard behind how generators and motors are nameplate-rated in kVA rather than kW. - IEC 60034-1 — Rotating electrical machines, Part 1: Rating and performance — International Electrotechnical Commission
International rating standard for generators and motors that underlies the kVA-based sizing this calculator explains.