Select secondary voltage, primary voltage, primary turns or secondary turns, then enter the three shown quantities. This calculator uses the ideal AC winding-voltage ratio.

Ideal AC winding-voltage ratio. Use consistent RMS magnitudes across each winding; three-phase line voltages may require connection factors. This is not a transformer design or safety assessment.

Turns in the winding, not the number of coils.

Transformer Voltage Formula

For ideal AC windings sharing the same magnetic flux, voltage magnitudes follow the turns ratio:

Vâ‚› = Vâ‚š Nâ‚› / Nâ‚š

The other solve modes use Vp = Vs × Np/Ns, Ns = Np × Vs/Vp, and Np = Ns × Vp/Vs. Vp and Vs are winding voltages; Np and Ns are winding turns. Use RMS values consistently. Three-phase line voltages can differ from winding voltages depending on the connection.

Select the value to solve for, enter the three shown quantities, then select Calculate. Voltage magnitudes must be nonnegative and turns positive. Solving turns requires positive voltages; two zero voltages do not determine a turns ratio.

Common Unit Conversions

QuantityUnitBase Unit Conversion
Voltage1 kV1,000 V
Turns1 turnOne winding loop

Secondary Voltage for Selected Turns Ratios

Primary voltageSecondary/primary turnsSecondary voltage
240 V1/2120 V
120 V2240 V
12 kV1/50240 V
24 V124 V

Example Calculations

Example 1: Find secondary voltage

With 240 V, 800 primary turns and 100 secondary turns: Vs = 240 × 100/800 = 30 V.

Example 2: Find primary turns

With 120 V primary, 12 V secondary and 50 secondary turns: Np = 50 × 120/12 = 500 turns.

FAQ

Does this predict loaded voltage exactly?

No. This ideal ratio omits losses, regulation and core behavior. Use manufacturer data for an actual device.

Can a calculated turns count be fractional?

A theoretical ratio may give a fractional count. The calculator does not round it into a construction recommendation.

Can voltage be zero?

Zero input gives zero output in the forward ratio. Zero voltage cannot establish a unique turns count. This tool does not assess electrical safety or transformer design.