Transformer turns per volt calculation with Example

Today in this post you will learn about the transformer turns per volt calculation formula with complete explanation. This transformer formula help you calculate the transformer turn per volt.

transformer turns per volt calculation

Transformer turns per volt calculation winding formula

To calculate the transformer turn per volt, First you need to calculate the bobbin size. For example if you have bobbin with length of 2? (inches) and width 3? inches. Then you need first to change the bobbin area to the Square inches.

So for that
2 x 3 = 6
So your total bobbin area in square inches is 6 square inches.
So to find out the turn per volt the formula is …
7.5 / total are of core/bobbin in square inches.
So 7.5/6 = 1.25

So the 1.25 is our turn per volt for 2? and 3 inches Bobbin or Core.
Now take another example if we want to design a step down transformer which step down the voltage from 220 to 12 Volts.

So our primary voltage is 220 VAC and our requirements on secondary is 12 Volts VAC.

So our turn per volts for core is 1.25

So 1.25 x primary voltage
1.25 x 220 is 275 . So 275 turn will be for the primary.

Our Secondary requirements is 12 Volts.
1.25 x 12 = 15 turn. So our secondary turn will be 15 for 12 VAC.


I hope the turn per volt formula help you to design a transformer. In this post I explained the transformer turn per volt formula. Now if you have any question according this post then you can ask me by using the below commenting system. Thanks for visiting and if you got some knowledge then place share this post with your friends on social media.

Also read :

Single phase submersible motor starter wiring diagram

Sikandar Haidar

The man behind this blog is called Sikandar Haidar who love to share and learn knowledge about electrical & electronics, sharing diagrams about single phase, 3 phase, RAC, HVAC, Controlling and much more...

6 thoughts on “Transformer turns per volt calculation with Example

  • February 9, 2019 at 5:38 am

    What about the AMP rating about above fourmula?

  • August 18, 2019 at 11:29 pm

    Nice topic
    What about toroidal transformer ?
    What is the good formula ?

  • July 3, 2020 at 12:20 pm

    Why you take 7.5 in this formula & what is this come from

  • April 20, 2021 at 7:11 pm

    Where does the number 7.5 come from?


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