KVA Calculator
KVA (kilovolt-amperes) measures the apparent power in an electrical system. It is what transformers, generators, and UPS systems are rated in because they must handle the full current regardless of the power factor. A single-phase 240V circuit drawing 50 amps has an apparent power of 12 kVA. This calculator also converts to real power (kW) and reactive power (kVAR).
The formulas:
- Single-phase: kVA = V × I / 1,000
- Three-phase: kVA = √3 × V × I / 1,000
kVA vs. kW vs. kVAR:
These three form a power triangle:
- kVA (apparent power): The total power the system must deliver, including both useful and wasted components. This is what sizes your transformer or generator.
- kW (real power): The portion that does actual work (lights, heat, motion). kW = kVA × power factor.
- kVAR (reactive power): The portion that shuttles back and forth between the source and inductive/capacitive loads. It does not do useful work but still requires current capacity.
Why kVA matters for equipment sizing:
A generator rated at 100 kW with a power factor of 0.8 actually needs to be a 125 kVA unit. If you size it at 100 kVA, the generator will be overloaded even though the real power draw is within its kW rating. This is because the generator's windings and cooling system must handle the full current, not just the real power component.
Common equipment ratings:
| Equipment | Typical Rating |
|---|---|
| Residential transformer | 25-50 kVA |
| Small commercial transformer | 75-500 kVA |
| Standby generator (home) | 10-20 kW / 12-25 kVA |
| UPS for server rack | 3-10 kVA |
| Industrial motor starter | 50-500 kVA |