Transformer Turns Ratio Calculator
Find the secondary voltage, secondary current and turns ratio of an ideal transformer from its primary voltage and winding turns.
V
turns
turns
A
Step-down transformer
- 1
Turns ratio a = Np ÷ Ns
500 ÷ 100 = 5 - 2
Secondary voltage Vs = Vp × Ns ÷ Np
230 × 100 ÷ 500 = 46
How does this calculator work?
For an ideal transformer the turns ratio a = Np/Ns sets everything: secondary voltage Vs = Vp × (Ns/Np) and, with primary current Ip given, secondary current Is = Ip × (Np/Ns) from power conservation Vp×Ip = Vs×Is. More secondary turns means step-up voltage and lower current.
Formula
How this is calculated
An ideal transformer relates primary and secondary windings through their turns ratio a = Np/Ns, where Np is the number of primary turns and Ns the number of secondary turns. Enter the primary voltage Vp (in volts) and both turn counts to obtain the secondary voltage Vs = Vp × (Ns/Np). When Ns > Np the device steps the voltage up (a < 1); when Ns < Np it steps it down (a > 1).
If you also supply the primary current Ip (in amperes), the calculator uses ideal power conservation Vp × Ip = Vs × Is to find the secondary current Is = Ip × (Np/Ns). Voltage scales with the turns ratio while current scales inversely, so a step-up in voltage means a proportional step-down in current. The primary current field is optional; leave it blank to compute voltage and ratio only.
This model assumes a lossless transformer with perfect magnetic coupling and no leakage, winding resistance, or core losses, so the computed efficiency is 100%. Real transformers run slightly below this. Both turn counts must be non-zero to avoid division by zero, and all turn values are treated as positive integers in practice even though decimals are accepted.
Frequently asked questions
The turns ratio a equals the number of primary turns divided by the number of secondary turns (Np/Ns). It also equals the voltage ratio Vp/Vs and the inverse of the current ratio Is/Ip for an ideal transformer.
If there are more secondary turns than primary turns (Ns > Np), the secondary voltage is higher and it is a step-up transformer. If Np > Ns, the secondary voltage is lower, making it a step-down transformer.
An ideal transformer conserves power: Vp × Ip = Vs × Is. When the secondary voltage drops, the secondary current must rise by the same factor to keep the power product constant.
Also known as
TG we-Calculate Editorial Team. (2026). Transformer Turns Ratio Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/transformer-turns-ratio-calculator
TG we-Calculate Editorial Team. "Transformer Turns Ratio Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/transformer-turns-ratio-calculator.
TG we-Calculate Editorial Team, "Transformer Turns Ratio Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/transformer-turns-ratio-calculator
@misc{wecalculate_transformer_turns_ratio_calculator, title = {Transformer Turns Ratio Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/transformer-turns-ratio-calculator}}, year = {2026}, note = {TG we-Calculate} }
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