kVA to Amps Calculator

kVA to amps calculator formula

A kVA to amps calculator turns the apparent power of a transformer or generator into the current it carries. Single-phase amps = kVA × 1,000 ÷ volts. Three-phase amps = kVA × 1,000 ÷ (volts × √3), where √3 is about 1.732. This calculator shows both answers at once.

The formula in plain words

kVA means thousands of volt-amps. Multiply by 1,000 to get volt-amps. Divide by the voltage to get amps, which gives you the single-phase answer. For three-phase, divide once more by 1.732, because the load is shared over three lines.

Worked examples

These match the calculator exactly.

1. Small single-phase transformer: 10 kVA at 240 V

• Volt-amps: 10 × 1,000 = 10,000
• Single-phase: 10,000 ÷ 240 = 41.67 A
• Three-phase: 10,000 ÷ (240 × 1.732) = 24.06 A

2. Commercial three-phase transformer: 75 kVA at 208 V

• Volt-amps: 75,000
• Three-phase: 75,000 ÷ (208 × 1.732) = 208.18 A
• If it were treated as single-phase: 75,000 ÷ 208 = 360.58 A

The second example shows how large the gap gets. Always choose the row that matches your supply.

Full-load amps at 240 V and 480 V

kVA	Single-phase at 240 V	Three-phase at 480 V
5	20.8 A	6.0 A
10	41.7 A	12.0 A
25	104.2 A	30.1 A
50	208.3 A	60.1 A
75	312.5 A	90.2 A

These are full-load current. They do not include the allowance that code adds for continuous loads.

Where you will use this

Transformer nameplates and generator labels are written in kVA, while wiring, breakers and meters work in amps. The conversion bridges the two. A nameplate that says 25 kVA, 240 V single-phase tells you the secondary can carry about 104 A before it is overloaded.

For a generator, kVA tells you the supply’s limit, while the work it can do depends on kW and power factor. If the appliances you plan to run are listed in watts, the watts to amps calculator goes the other way.

Worked example in reverse

Suppose a nameplate says 30 kVA and the supply is three-phase at 480 V. Amps = 30,000 ÷ (480 × 1.732) = 36.08 A. If you wanted the same 30 kVA at 240 V three-phase, the current doubles to 72.17 A, because halving the voltage doubles the current for the same power. Higher voltage means thinner wire for the same load, which is why long runs and big motors use 480 V.

You can also run the formula backward. A 100 A single-phase feed at 240 V carries 100 × 240 ÷ 1,000 = 24 kVA.

Choosing single-phase or three-phase

Most homes have single-phase service, 240 V across the two hot legs. Shops, farms and commercial buildings often have three-phase service at 208 V or 480 V. Look at the transformer nameplate or ask the utility. A nameplate normally prints the phase count next to the kVA rating.

Reading a nameplate

Look for three numbers on a transformer or generator label: kVA, voltage and phase. Some also list the rated amps for each side. If the label amps and your calculation differ by a few percent, that comes from rounding or voltage tolerance. A big difference means you read the wrong voltage or phase. Check the primary and secondary separately, since each side has its own voltage and so its own current.

Common mistakes

• Using single-phase math on a three-phase service. The current will be about 73 percent too high.
• Entering line-to-neutral voltage for three-phase.
• Treating kVA as kW. Multiply by the power factor to get kW.
• Using full-load amps as the breaker size. Protective devices follow code and the equipment’s instructions.

Electrical work carries a risk of shock and fire. Have a licensed electrician size and install anything that connects to a service.

Related pages

Convert load details with the amps to watts calculator. For backup power, see the generator size calculator. To check the protective device, use the breaker size calculator.

Power factor in one example

A 10 kVA supply feeding a motor with a power factor of 0.8 delivers 10 × 0.8 = 8 kW of real power. The wires still carry the full 41.67 A at 240 V single-phase, because current follows kVA. This is why a nameplate gives kVA: the conductors and windings must handle the current whether or not it does useful work.