3-Phase Power Calculator

Almost every UK commercial supply above the smallest shop is three-phase, so the maths underpinning kW, kVA and amps is the maths underpinning every capacity decision you make. A finance lead approving a new compressor, a chiller, an EV charger array or a CNC machine is, whether they realise it or not, betting that the kW load fits inside the kVA capacity of the supply and the breaker protection on the panel. Get the three-phase conversion wrong and you either trip the head of the building or pay for a connection uplift you did not need.

Power factor is the variable that catches out most non-electrical decision makers. A 100 kW load at 0.85 power factor draws 118 kVA from the supply and roughly 170 amps per phase at 400 V, but the supplier still bills the kW for energy and the kVA (or reactive kVArh) for capacity charges. That gap between nameplate kW and supply-side kVA is exactly where DUoS capacity charges and reactive-power penalties accumulate. Knowing how to translate between the three figures makes it possible to spot a bill anomaly, sanity check a quote, or justify a capacitor bank.

For Purely Energy clients, the three-phase conversion is the bridge between the engineering side of the site and the procurement side of the bill. When we review a multi-site account, the first question is almost always whether the MIC is sensibly matched to actual kW demand, and the second is whether the power factor is high enough to avoid reactive charges. Both questions need the kW, kVA and amps to be reconciled against meter data. Use this calculator to translate between them quickly, and to spot mismatches before they become a written-off capacity uplift.