Transformer Turns Ratio Calculator
Enter the primary and secondary winding turns and a primary voltage to find the turns ratio and resulting secondary voltage.
How transformer turns ratio works
A transformer's turns ratio is the number of turns in the primary winding (Np) divided by the number of turns in the secondary winding (Ns). This same ratio also relates the primary and secondary voltages: Vp/Vs = Np/Ns, so Vs = Vp × (Ns/Np).
A ratio greater than 1:1 (more primary turns than secondary) is a step-down transformer, reducing voltage — common in power adapters. A ratio less than 1:1 is a step-up transformer, increasing voltage, as used in some power distribution equipment.
Frequently asked questions
What's the difference between a step-up and step-down transformer?
A step-down transformer has more primary turns than secondary turns, reducing the output voltage. A step-up transformer has more secondary turns than primary turns, increasing the output voltage.
Does the turns ratio also apply to current?
Yes, but inversely — for an ideal transformer, Ip/Is = Ns/Np, the opposite of the voltage relationship. A step-down transformer that reduces voltage proportionally increases current on the secondary side.
Is this calculation accurate for real transformers?
This gives the ideal transformer relationship, assuming no losses. Real transformers have some energy loss from winding resistance and core effects, so actual secondary voltage under load may be slightly lower than calculated.