This transformer conductor size calculator finds the wire cross-section needed for a winding from its current and a chosen current density. Enter the values above to size the conductor.
Formulas
Current I = VA ÷ (√3 × VL) (three phase) Wire area A = I ÷ current density (A/mm²)
Example
10 kVA, 400 V, 3-phase: I = 14.4 A; at 2.3 A/mm², area = 14.4 ÷ 2.3 = 6.3 mm².
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Frequently Asked Questions
How do I size transformer winding wire?
Divide the winding current by a safe current density, often 2 to 3 A/mm2, to get the conductor cross-section.
What current density should I use?
2 to 3 A/mm2 is typical for copper windings; lower density runs cooler but uses more copper.
Does this apply to both windings?
Yes. Use each winding’s own current with the same method to size primary and secondary conductors.