Transformer kVA Sizing Calculator
Estimate a transformer rating from user-entered apparent load demand and a selected headroom percentage.
Enter transformer values
Capacity estimate
Selected rating meets this arithmetic estimate.
About this calculator
Estimate a transformer rating from user-entered apparent load demand and a selected headroom percentage.
Load demand must already be established by the user. This page does not calculate demand, diversity, code loads, motor starting, or a universal standard-size recommendation.
Method and assumptions
Estimated required kVA = entered load demand × (1 + headroom percentage ÷ 100). The selected transformer rating is compared with that result and the difference is shown.
Ideal ratio and capacity arithmetic do not include winding losses, temperature rise, harmonics, load diversity, or equipment-specific limits unless stated in the input model.
FAQs
Does this determine a complete transformer installation?
No. It performs the displayed arithmetic only. Verify the transformer nameplate, manufacturer application data, connections, protection, conductors, and locally adopted requirements separately.
Can I use line-to-line voltage as winding voltage for every three-phase transformer?
No. Use the actual winding voltage or turns data. Three-phase line-voltage ratios depend on winding connections and are not always equal to individual winding turns ratios.
Sources
Ideal transformer relationships, entered nameplate and test values, and the calculation conventions described above.