Transformer Turns Calculator
A transformer's turns ratio directly sets its voltage ratio — more turns on one side than the other steps voltage up or down by exactly that proportion, with no moving parts.
Inputs
Result
60 V secondary
Turns ratio 4 : 1
How the transformer turns calculator works
Turns ratio = primary turns ÷ secondary turns.
Secondary voltage = primary voltage ÷ turns ratio.
Worked example: 1,000 primary turns, 250 secondary turns, 240 V primary
- Turns ratio = 1,000 ÷ 250 = 4 : 1.
- Secondary voltage = 240 ÷ 4 = 60 V.
Common mistakes to avoid
Assuming secondary current scales the same direction as voltage
Ideally, power is conserved across a transformer, so as voltage steps down, current steps up by the same ratio (and vice versa) — a step-down transformer doesn't just lower voltage for free, it proportionally raises available current.
Forgetting real transformers have some power loss
This ideal calculation assumes 100% efficiency. Real transformers lose a small percentage to resistance and core losses, so actual secondary voltage under load is slightly lower than this calculation predicts.
Frequently asked questions
How do I find secondary current if I know primary current?
In an ideal transformer, primary voltage × primary current = secondary voltage × secondary current (power is conserved), so secondary current = (primary voltage × primary current) ÷ secondary voltage.
What does a turns ratio of exactly 1:1 mean?
The transformer is an isolation transformer — same voltage on both sides, used to electrically isolate a circuit rather than change voltage.
Is a step-up transformer just this calculator in reverse?
Yes — if secondary turns exceed primary turns, the turns ratio is less than 1 and secondary voltage comes out higher than primary voltage, the step-up case.
Does this work for three-phase transformers?
This is the single-phase turns-ratio relationship; three-phase transformer configurations (delta, wye) add extra factors depending on winding arrangement.
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