How to Calculate Transformer KVA?

Transformer sizing always ends in kVA. This article gives you the formulas for single phase and three phase systems, worked examples, and a reference table of common distribution ratings.

The key point: kVA is apparent power. It depends on voltage and current, not on how efficiently the load converts electricity into work.

Transformer sizing always ends in kVA. This article gives you the formulas for single phase and three phase systems, worked examples, and a reference table of common distribution ratings.

The key point: kVA is apparent power. It depends on voltage and current, not on how efficiently the load converts electricity into work.

kVA = (V × I) ÷ 1,000, where V is the voltage in volts and I is the current in amperes.

Example: a single phase load drawing 200 A at 230 V is (230 × 200) ÷ 1000 = 46 kVA.

kVA = (√3 × V × I) ÷ 1,000 = (1.732 × V × I) ÷ 1,000, where V is the line-to-line voltage.

Example: a three phase load drawing 700 A at 400 V is (1.732 × 400 × 700) ÷ 1000 = 485 kVA.

kVA = kW ÷ power factor. A 500 kW load at 0.8 power factor needs a 625 kVA transformer.

This is why power factor correction matters: improving PF from 0.8 to 0.95 on a 500 kW load reduces the required transformer capacity from 625 kVA to 526 kVA.

Invert the same formula: a 1000 kVA transformer at 400 V can supply 1443 A continuously. At 0.85 power factor that is about 850 kW of real load, before any diversity or growth allowance.

Not sure which rating fits your project? Send us your load list and we will size it for you, or email info@xsdfftransformer.com, call +86 158 6789 7761 or WhatsApp +852 5416 2620.