Transformer Turns Ratio Calculator
Calculate turns ratio, voltage, current, and impedance transformation for an ideal transformer. Step-up and step-down applications.
How to Use
- Enter primary and secondary turns, or voltage ratio.
- See transformed voltages, currents, and impedance ratio.
- Transformer is assumed ideal (lossless, fully coupled).
Show Work
Formulas
History of the Turns Ratio
The turns-ratio equation V2/V1 = N2/N1 is a direct consequence of Faraday\'s 1831 law of electromagnetic induction. Each turn of a coil encloses the same changing flux, so the voltage induced per turn is the same for both windings on a common core. Stack up N1 turns on the primary and the total induced voltage is N1 times the per-turn voltage; N2 turns on the secondary gives N2 times the same per-turn voltage. The ratio falls out immediately.
Practical use of the turns ratio for industrial voltage transformation dates to the 1880s. Westinghouse\'s 1886 Great Barrington demonstration used Gaulard-Gibbs transformers with about 10:1 step-down ratios to take distribution-line voltage down to lighting-circuit voltage. Edison\'s direct-current rival system had no equivalent mechanism — transformers only work for alternating current — which is why AC won the "War of the Currents."
Impedance matching through turns ratios appeared in early telephony. The Bell system used audio transformers to match the few-hundred-ohm impedance of carbon microphones and the long-line impedance of twisted-pair copper to the ~1000Ω impedance of moving-iron receivers. The same principle still drives tube-amplifier output transformer design and RF balun construction today — the physics hasn\'t changed, only the scale and operating frequency.
About This Calculator
Enter primary and secondary turn counts, a primary voltage, and a secondary load impedance. The calculator returns the turns ratio, the resulting secondary voltage, the impedance ratio (N1/N2)², and the reflected impedance seen on the primary side — the two most commonly needed transformer quantities for audio, RF, and power work.
The math is ideal. Real transformers have ~1–5% loss, leakage inductance that degrades high-frequency response, winding capacitance that causes resonances, and core saturation that limits flux density. For critical designs, simulate with a measured equivalent-circuit model rather than trusting ideal math alone. Everything runs client-side; no values leave your browser.
About the Transformer Turns Ratio Calculator
The Transformer Turns Ratio Calculator is a free tool for electronics and circuit design. It runs right in your web browser, so there is nothing to download. Calculate turns ratio, voltage, current, and impedance transformation for an ideal transformer. Step-up and step-down applications.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
What does turns ratio do?
Primary and secondary voltage are proportional to turn counts: V2/V1 = N2/N1. Currents invert: I2/I1 = N1/N2. Impedance transforms as the square: Z2/Z1 = (N2/N1)².
Why step-up/step-down?
Power transmission benefits from high voltage / low current (less I²R loss in wires). Consumer devices need lower voltage for safety. Transformers convert between them with >95% efficiency.
Impedance matching?
A transformer with N1:N2 turn ratio makes a load Z2 on the secondary appear as Z1 = Z2·(N1/N2)² on the primary. Used to match audio amps to 4/8Ω speakers, or 50Ω RF to antenna impedance.
How do I use the Transformer Turns Ratio Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Wall Adapter
Step-down 120V → 12V uses 10:1 turns ratio (modern ones use switchers, but the principle is the same in isolation transformers).
Audio Output Transformer
Match tube amp's high-impedance plate (~4kΩ) to 8Ω speaker: turn ratio √(4000/8) ≈ 22:1.
Antenna Balun
1:1 transformer converts unbalanced (coax) to balanced (dipole) signal.
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