kVA to Amps Calculator

Find the full-load current per phase of a transformer, UPS or generator from its kVA rating and output voltage.

Inputs

Result

Enter the kVA rating to see the current.

Related tools

How the calculation works

The current at a given apparent power depends only on the voltage and the circuit type:

Single-phase: amps = kVA × 1,000 ÷ volts
Three-phase: amps per phase = kVA × 1,000 ÷ (√3 × volts), with the line-to-line voltage and √3 ≈ 1.732

Entering the nameplate kVA gives the full-load current (often abbreviated FLA on nameplates), the current per phase when the unit runs at its rating. No power factor is needed: kVA is volts × amps, so it does not depend on one. If you start from a load in kW, convert it to kVA first.

The default is 480 V three-phase, a common output voltage for generators, large UPS systems and the primary side of datacenter transformers in North America. Change it for 208 V, 400 V or 415 V equipment, or for single-phase units.

480Y/277 V nameplates. A transformer secondary or generator labeled 480Y/277 V has 480 V between any two phases (line-to-line) and 277 V from each phase to neutral (480 ÷ √3, line-to-neutral). The 277 V is commonly used for lighting circuits. For full-load current, enter 480 V with three-phase selected.

Worked example

A 500 kVA standby generator with a 480 V three-phase output:

amps per phase = 500,000 ÷ (1.732 × 480) = 500,000 ÷ 831.4 = 601.41 A

The same 500 kVA at 208 V three-phase:

amps per phase = 500,000 ÷ (1.732 × 208) = 1,387.86 A

More than twice the current for the same kVA, which means larger conductors and switchgear at the lower voltage.

Frequently Asked Questions

What is the full-load current of a 500 kVA transformer at 480 V?

500,000 ÷ (1.732 × 480) = 601.41 A per phase on a 480 V three-phase secondary. At 208 V the same 500 kVA is 1,387.86 A per phase, which is one reason large loads are often distributed at 480 V and stepped down close to the racks.

Why is there no power factor input?

kVA is already volts × amps (× √3 on three-phase), so the current follows from the kVA and the voltage alone. Power factor matters only when you start from kW: convert kW to kVA first, or use the kW to amps calculator.

Are the primary and secondary currents of a transformer different?

Yes. The kVA is the same on both sides, less small losses, so the current scales inversely with the voltage. A 75 kVA transformer stepping 480 V down to 208Y/120 V carries about 90.21 A per phase on the 480 V side and 208.18 A per phase on the 208 V side at full load.

Is full-load current the breaker size?

No. It is the current at the rated kVA. Breaker and conductor sizes for a transformer, UPS or generator follow the applicable electrical code and the manufacturer's instructions, which can call for ratings above full-load current.