Transformer Size Calculator
Estimate transformer kVA and round up to a common standard rating.
Recommended transformer rating
Enter values
Planning estimate: recommended standard kVA is rounded upward from demand kVA plus the selected spare margin. Final transformer selection must check load profile, motor starting, harmonics, future growth and utility requirements.
How this calculator works
Demand kVA = Demand kW / PF.
Design kVA = Demand kVA × (1 + spare margin).
The calculator then rounds upward to the next rating in its common planning list.
Example
An 800 kW maximum demand at 0.9 PF is about 889 kVA before adding spare capacity.
Frequently asked questions
Why add spare capacity?
A margin can provide room for future load growth and uncertainty, but excessive oversizing can also be undesirable.
Does this handle harmonic loads?
No. Significant harmonics may require transformer derating or a specially selected transformer.
Is the recommended rating always available?
Standard product ratings vary by manufacturer and utility. Verify the selected rating before procurement.