Why does three phase use √3?
The balanced line-to-line three-phase apparent-power relationship includes √3.
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Transformer kVA Calculator — Single & Three Phase Load Sizing
Calculate load kVA from voltage and current for single or balanced three-phase systems, then apply an explicit spare-capacity percentage.
Result
83.138 kVA
69.282 kVA calculated load
Includes 20% entered spare capacity · balanced 3φ VLL formula.
Formula and worked example
1φ kVA=V×I/1000; balanced 3φ kVA=√3×VLL×I/1000; planned kVA=load kVA×(1+spare%).
400 V, 100 A balanced three-phase is about 69.28 kVA; 20% entered spare capacity gives 83.14 kVA planning load.
Assumptions
- Three-phase voltage is line-to-line and load is balanced.
- This does not select a standard transformer or protection settings.
Last updated: 2026-09-16
Frequently asked questions
Is spare capacity mandatory?
No. It is an explicit planning input, not a universal requirement.