The calculation, without hidden assumptions
For an ideal transformer, the primary-to-secondary voltage ratio follows the winding-turns ratio: Vp/Vs = Np/Ns. This calculator lets you choose any one of those four quantities as the unknown instead of forcing one fixed workflow. It then reports the ratio, whether the entered relationship represents a voltage step-up or step-down, and the ideal inverse current-ratio relationship while keeping real transformer regulation and losses outside the model.
How to use this calculator
Choose which of the four transformer quantities you want to solve.
Enter the other three known values. The selected target field is ignored by the calculation and replaced by the solved value.
Check the primary:secondary ratio and step-up/step-down label, then compare against actual nameplate/tap information for real equipment.
Where people use it
- •Transformer theory and winding-ratio checks
- •Estimating an unknown winding turn count
- •Checking ideal primary/secondary voltage relationships
Example: 240 V primary, 24 V secondary, 1,000 primary turns
The ideal ratio is 10:1. Secondary turns = 1,000 × 24 ÷ 240 = 100 turns.
What the result does not assume
- •The ratio relationship is an ideal model. Real output voltage can differ because of winding resistance, leakage reactance, regulation, taps and load.
- •Turns ratio alone does not design a transformer winding; core area, flux density, frequency, insulation, temperature rise and other constraints remain separate.
Frequently asked questions
Is transformer voltage ratio the same as turns ratio?+
In the ideal transformer model, Vp/Vs = Np/Ns. Real measured voltages can differ from the ideal ratio under load.
Does a 10:1 turns ratio always mean step-down?+
With the primary-to-secondary convention Np:Ns = 10:1, the ideal secondary voltage is one tenth of the primary voltage.
Can this determine wire gauge or winding construction?+
No. It only solves the ideal ratio relationship and does not perform physical transformer design.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
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