How Transformers Work

A transformer transfers electrical energy between two circuits through electromagnetic induction. The voltage and current ratios are determined by the turns ratio — the number of windings in the primary vs secondary coil.

The Turns Ratio Formulas

Turns Ratio (n) = N_primary / N_secondary = V_primary / V_secondary = I_secondary / I_primary

• Step-up transformer: n < 1 (secondary has more turns), voltage increases.
• Step-down transformer: n > 1 (primary has more turns), voltage decreases.
• Isolation transformer: n = 1, same voltage but galvanic isolation.

Power is conserved (ignoring losses): P_primary ≈ P_secondary, so higher voltage means lower current.

How to Use This Calculator

Enter the primary voltage and desired secondary voltage to get the turns ratio. Or enter the turns ratio and one side's voltage to calculate the other. The calculator also computes secondary current from primary current and handles impedance transformation.

Practical Examples

Example 1: 230V primary, 12V secondary. n = 230/12 = 19.17:1. If primary draws 100mA, secondary delivers 100 × 19.17 = 1.917A.

Example 2: Impedance matching for audio amp: 8Ω speaker load to 3,200Ω tube amp output. n = √(3200/8) = 20:1 turns ratio.

Applications

Transformers power everything from wall adapters to national grid transmission — stepping up for efficient long-distance transmission and stepping down for safe domestic use.