Three-Phase Converter Calculator
Convert kW, kVA and amps between single and three phase.
For three phase, this is the current in each line conductor (equal in a balanced system) - not a per-phase-then-summed total.
For guidance only. These calculators are planning aids for licensed electrical workers and inspectors. All results must be independently verified against the current editions of AS/NZS 3000:2018, AS/NZS 3008.1.2, and other applicable standards before being relied on for any installation. CertMate accepts no responsibility or liability for any work carried out, decisions made, or certification issued in reliance on these results. The certifying electrical worker remains solely responsible for compliance with the Electricity (Safety) Regulations 2010 and all applicable New Zealand law.
The conversion every commercial job needs eventually
Equipment nameplates, generator spec sheets and switchboard schedules all describe load differently - sometimes in kW, sometimes kVA, sometimes just amps. Converting between them properly means bringing in power factor and, for three-phase, the phase geometry that connects line current to total power.
It's not a complicated calculation once you've got the right formula in front of you, but it comes up constantly enough on commercial and industrial jobs that having it as a quick reference beats re-deriving it each time.
Worked examples
Three-phase motor load, checking supply current
A motor rated in kW at a typical inductive power factor, on a standard 400V three-phase supply. This is the everyday case - confirming what current a motor's kW rating actually translates to before deciding on cable and breaker sizing.
Generator sizing for a commercial fit-out
A commercial fit-out's total load expressed in kVA on the generator spec sheet, needing to be checked against the actual kW demand once realistic power factor is applied - generators are usually specified by kVA, but the useful comparison against building load is in kW.
Single-phase equipment on a mixed-supply job
A single-phase piece of equipment on an otherwise three-phase commercial supply, where you need the straightforward single-phase current from its kW rating without the √3 factor that the three-phase side of the same job requires.
Frequently asked questions
What's the difference between kW and kVA?
kW is real power - the power actually doing useful work. kVA is apparent power - the total power the supply has to deliver, including the portion that doesn't do useful work due to power factor. They're equal only at a power factor of 1.0; for any real motor or inductive load, kVA is always somewhat higher than kW.
Where do I get the power factor for a piece of equipment?
It's usually on the equipment nameplate alongside the kW or kVA rating. If it's not stated, 0.8 is a common rule-of-thumb assumption for general motor loads, but use the actual nameplate value where you can - it varies enough between equipment to matter for sizing decisions.
Why does the √3 factor appear for three-phase but not single-phase?
In a balanced three-phase system, the relationship between line voltage, phase current and total power involves the square root of 3 because of how the three phases combine vectorially. Single-phase doesn't have that geometry, so the conversion is simpler - just voltage times current.
What's this calculator most useful for on the job?
Working out what current a given kW or kVA load will actually draw on a three-phase supply, or the reverse - confirming what a measured current corresponds to in kW when you're sizing a submain, checking a generator's capacity, or specifying equipment for a commercial fit-out.
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