Transformer Turns Ratio Calculator
Calculate the turns ratio Np:Ns from winding counts or from primary and secondary voltages.
How it works
- 1Choose to calculate from winding turns (Np, Ns) or from voltages (Vp, Vs).
- 2Enter the two values — the turns ratio Np:Ns equals the voltage ratio Vp:Vs.
- 3Read the ratio, the transformer type, and the inverse ratio.
Use cases
- Verifying the winding spec of a mains transformer for a power supply.
- Checking whether a transformer is step-down or step-up before connecting equipment.
- Deriving the secondary turns needed for a target output voltage.
Frequently asked questions
What is the transformer turns ratio?
The turns ratio is Np ÷ Ns. By Faraday’s law it equals the voltage ratio Vp ÷ Vs, so a 1000:250 winding steps voltage down by 4:1.
When is a transformer step-down vs step-up?
A ratio greater than 1 (Np > Ns) is step-down; less than 1 is step-up; exactly 1 is an isolation transformer.
Can I use voltages instead of turns?
Yes. Because Vp/Vs = Np/Ns, the open-circuit primary and secondary voltages give the same ratio.
Related tools
See all →Find the gear ratio, output speed, torque, and mechanical advantage of a gear pair, in metric or imperial.
Calculate the overall ratio and output speed of a multi-stage compound gear train.
Calculate shaft torque from power and rotational speed in metric or imperial units.
Calculate the mechanical power transmitted by a rotating shaft from torque and shaft speed.