Transformer Turns Calculator
Work out transformer turns ratio, primary or secondary voltage and current from winding turns free in your browser with this transformer calculator.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the primary and secondary voltages and primary turns.
- Press Calculate.
How it works
Secondary turns = primary turns × secondary voltage ÷ primary voltage — the turns ratio matches the voltage ratio.
Worked example
240 V → 12 V, 1,000 turns. = 50 secondary turns.
Common mistakes
- Swapping primary and secondary — put the input on the primary side of the ratio.
- Assuming an ideal transformer loses nothing; real units have copper and core losses.
Frequently asked questions
How does the turns ratio work?
Voltage ratio equals turns ratio: Vp ÷ Vs = Np ÷ Ns. A 240 V to 12 V transformer has a 20:1 turns ratio.
What happens to current in a transformer?
Current changes inversely to voltage — step the voltage down 20:1 and the available current steps up about 20:1, minus losses.
Does this work for step-up transformers too?
Yes — if the secondary voltage is higher than the primary, you get more secondary turns. The turns ratio always matches the voltage ratio.
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Cite this tool
Zerdly. (2026). Transformer Turns Calculator. Retrieved from https://www.zerdly.com/tools/transformer-turns-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.