kVA to Amps Calculator

How to convert kVA to amps

Because kVA already accounts for the power factor, you only need the voltage and the number of phases.

Single phase: multiply the kVA by 1000 to get VA, then divide by the voltage.
3 phase: multiply the kVA by 1000, then divide by √3 (1.732) × the line-to-line voltage.

Quick rules of thumb

• 3 phase 400V: roughly 1.44A per kVA, per phase.
• Single phase 230V: roughly 4.35A per kVA.

So a 20 kVA generator on a 3 phase 400V supply delivers about 29A per phase, and a 100 kVA generator about 144A per phase.

What does "amps per phase" mean?

On a 3 phase supply the load is shared across three live conductors. The figure from a kVA to amps per phase calculation is the current flowing in each of those conductors. It isn't a total to split three ways. Don't add the three phases together: a 100 kVA 3 phase generator is rated at about 144A per phase, not 433A.

Why the amps matter when choosing a generator

The kVA rating tells you how much power a generator can supply. The amps tell you what the rest of the installation has to be rated for:

• Output breaker and protection: sized to the generator's full-load current.
• Cables: the cable size from the generator to your distribution board depends on the current, cable length and installation method.
• ATS panels and changeover switches: rated in amps. A standby generator's automatic transfer switch must be rated at or above the generator's full-load current, so for a 100 kVA, 400V set (144A per phase) you'd choose the next standard rating up, typically 160A.
• Site distribution: temporary site distribution boards and sockets are rated in amps too, including 110V tool circuits.

Your electrician or electrical designer will confirm cable and protection sizes. Converting kVA to amps first gives you the numbers to start that conversation.

Single phase or 3 phase?

UK homes and small businesses usually have a single phase 230V supply. Larger commercial, agricultural and industrial sites usually have 3 phase 400V. Choose the phase that matches the supply you're backing up or the equipment you're powering. Browse 3 phase generators or single phase generators.