Transformer Turns Ratio Calculator
Calculate the turns ratio of an ideal transformer.
Find secondary voltage, secondary turns, or current ratio from the transformer equations.
How Transformer Turns Ratio Is Calculated
A transformer transfers electrical energy between circuits through electromagnetic induction. The turns ratio determines how voltage and current are transformed between primary and secondary windings.
Turns Ratio Formula:
N1/N2 = V1/V2 = I2/I1
Where:
- N1 = number of turns in primary coil
- N2 = number of turns in secondary coil
- V1 = primary voltage
- V2 = secondary voltage
- I1, I2 = primary and secondary currents (inverse relationship)
Ideal Transformer Power Conservation:
P_in = P_out → V1 × I1 = V2 × I2
Worked Example: Step-down transformer: primary 240V, secondary 12V for LED driver:
- Turns ratio = 240/12 = 20:1
- If secondary current = 5A, primary current = 5/20 = 0.25A
- Power = 12V × 5A = 60W (same on primary: 240V × 0.25A = 60W)
Common Transformer Applications:
| Application | Primary | Secondary |
|---|---|---|
| Power grid distribution | 11,000V | 240V |
| Wall adapter (phone charger) | 240V | 5–12V |
| Microwave oven | 240V | 2,000V |
| Welding transformer | 240V | 20–80V |
| Audio output transformer | 600Ω | 8Ω |
Real Transformer Efficiency: Large power transformers: 95–99% efficient. Small consumer transformers: 85–95%. Losses include copper loss (I²R heating in windings) and core loss (hysteresis + eddy currents in iron).