Transformer Turns Ratio Calculator
Turns ratio, secondary turns and current ratio from primary/secondary voltages.
Input
ℹ Turns ratio n = Vp/Vs = Np/Ns. Current ratio is the inverse.
Results
Turns Ratio—
Secondary Turns Ns—
Current Ratio—
💡 Usage & Formula
Vp/Vs = Np/Ns = Is/Ip = n. An ideal transformer conserves power: Vp·Ip = Vs·Is.
When you need it: Finding the turns ratio for a target voltage, or the impedance a load reflects to the primary, in a mains, audio, isolation or flyback transformer.
Worked example: 120 V→12 V gives Np/Ns = 10. Impedance reflects as the square of the ratio: an 8 Ω load through a 10:1 winding looks like 8 × 10² = 800 Ω at the primary.
Tips & gotchas:
- Voltage scales with the turns ratio; impedance scales with the ratio squared.
- The core must reset its volt-seconds each cycle or it walks into saturation and the current spikes.
- Real windings add resistance and leakage inductance — they cap efficiency and cause ringing.
- In a flyback the ratio also sets the switch's reflected voltage stress, so it's a safety-margin knob too.
📖 References:Transformer (Wikipedia)