Transformer Turns Ratio

Formula

Description

The transformer turns ratio is the ratio of the number of primary turns to secondary turns, which equals the voltage ratio in an ideal transformer. A turns ratio greater than 1 indicates a step-down transformer (reduces voltage), while less than 1 indicates step-up. This formula is placed in the inductors category to complement the mutual inductance formula. Transformers are fundamentally coupled inductors, and the turns ratio determines voltage transformation, current transformation (inverse ratio), and impedance transformation (square of the ratio).

Variables

• N — Turns ratio (primary to secondary)
• V₁ — Primary voltage (V)
• V₂ — Secondary voltage (V)

Practical Notes

For power transformers, account for regulation (voltage drop under load) by designing the no-load secondary voltage 5-10% higher than needed. The current ratio is the inverse: I₂/I₁ = N. Impedance reflects as Z_primary = N² × Z_secondary. Multiple secondaries allow different output voltages from one transformer.