Why convert kVA to amps
Transformers, generators and UPS units are rated in kilovolt-amperes (kVA), which is apparent power: the product of voltage and current with no regard for how much of it does useful work. Wires, breakers and fuses, however, are chosen by current in amperes. Converting from kVA to amps tells you how much current a device can deliver or draw at a given voltage, and therefore what conductor and protection it needs.
Enter the kVA rating, the line voltage and whether the supply is single-phase or three-phase. The calculator returns the current, the apparent power in volt-amperes, the real power in kW if you supply a power factor, and the current multiplied by 1.25. That last figure is a common starting point for sizing continuous loads, but always confirm the multiplier with your local electrical code.
Formula and variables
Single-phase: I = kVA × 1000 / V
Three-phase: I = kVA × 1000 / (√3 × V)
- I is the line current in amperes.
- kVA is the apparent power rating.
- V is the line-to-line voltage (for a single-phase circuit, the voltage across the two conductors).
- √3 is about 1.732 and comes from the 120-degree phase separation of balanced three-phase loads.
Real power in kW is kVA × power factor. Power factor does not change the current for a given kVA, because kVA already includes the reactive part.
Worked example
A 50 kVA three-phase transformer at 480 V, with a load power factor of 0.8.
- Denominator: 1.7321 × 480 = 831.38.
- I = 50,000 / 831.38 = 60.14 A.
- Real power = 50 × 0.8 = 40 kW.
- Times 1.25: 60.14 × 1.25 = 75.18 A.
Compared with a single-phase supply of the same size, 50,000 / 480 = 104.17 A, three-phase carries the same kVA at about 58% of the current. As a second check, 10 kVA at 240 V single-phase gives 10,000 / 240 = 41.67 A.
Common mistakes and how to interpret the result
- Using the wrong voltage. For three-phase, use the line-to-line value such as 208, 400 or 480 V, not the 120 or 277 V line-to-neutral value.
- Mixing kW and kVA. A 50 kW load at 0.8 power factor is 62.5 kVA, so it draws more current than 50 kVA would.
- Forgetting the phase setting. Leaving single-phase selected on a three-phase system overstates current by 73%.
- Treating the result as a full wire-sizing answer. Conductor size also depends on temperature rating, installation method, voltage drop and code rules.