Transformer Turns Ratio Calculator
Ideal transformer relationships — turns ratio from voltages or windings, secondary voltage and current, reflected impedance and power, with efficiency and regulation adjustments.
How it works
V_s / V_p = N_s / N_p; I_s / I_p = N_p / N_s (ideal); Z_reflected = Z_load × (N_p/N_s)²; P_in = P_out ÷ η
An ideal transformer conserves power and links voltage to turns: halve the turns, halve the voltage, double the available current. Impedance transforms by the square of the ratio, which is how a transformer matches an 8 Ω speaker to a valve amplifier or a 50 Ω antenna to a 300 Ω feed. Real transformers add copper and core losses (the efficiency input) and a few percent of voltage droop under load, so secondary voltages are specified at rated current.
Worked example
1,150 : 60 turns = 19.17 : 1, so 230 V becomes 12.0 V. A 4 Ω load draws 3.0 A (36 W); at 95% efficiency the primary takes 0.165 A and sees the load as 1,470 Ω.
Frequently asked questions
Does the turns ratio work for DC?
No — transformers need changing flux; DC produces no secondary voltage and can saturate the core.
Why 0.2 volts per turn?
Volts per turn is set by core area, flux density and frequency (V = 4.44·f·N·B·A); small mains transformers run 0.1–0.5 V/turn.
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This calculator is for educational purposes. Double-check important results before acting on them.