Transformer Sizing Calculator

Size a transformer two ways: from a known kVA, or from the secondary load you need to serve. Get the kVA and the primary and secondary full-load amps for single- or three-phase systems.

Transformer

Phase

Solve From

kVA

Primary Volts

Secondary Volts

Sizing

Transformer Size75 kVA

Primary FLA90.2 A

Secondary FLA208.2 A

Three-phase: A = VA ÷ (V × √3). Round up to the next standard transformer size and verify primary/secondary OCPD per NEC 450.3.

Three-phase amps = VA ÷ (V × √3); single-phase = VA ÷ V. Round up to the next standard transformer size and size primary/secondary overcurrent protection per NEC 450.3. For planning — confirm with the equipment spec.

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