Transformer Turns Ratio Calculator
Enter a voltage pair or a winding-turns pair to find the transformer turns ratio Np over Ns, which equals Vp over Vs. The calculator then derives the secondary voltage from the primary voltage and the secondary current from the primary current using the ideal transformer relations.
How to use the transformer turns ratio calculator
- Enter either the primary and secondary voltages, or the primary and secondary turns.
- Optionally enter the primary voltage to derive the secondary voltage.
- Optionally enter the primary current to derive the secondary current.
- Read the turns ratio and the transformed quantities.
Examples
120 V to 12 V step-down
primaryVoltage = 120, secondaryVoltage = 12, primaryCurrent = 2
turns ratio = 10, secondary current = 20 A
1000 to 100 turns
primaryTurns = 1000, secondaryTurns = 100
turns ratio = 10
Frequently asked questions
What is the transformer turns ratio formula?
The turns ratio equals the primary turns over the secondary turns, which also equals the primary voltage over the secondary voltage, Np / Ns = Vp / Vs. A 120 V to 12 V transformer has a ratio of 10.
How does the turns ratio affect current?
Current scales inversely with voltage, so the secondary current equals the primary current times the turns ratio, Is = Ip * (Np / Ns). A step-down transformer raises the secondary current.
What is the difference between step-up and step-down?
A step-down transformer has more primary turns than secondary turns, so the ratio is greater than 1 and the output voltage is lower. A step-up transformer has a ratio below 1 and a higher output voltage.
Do I need to enter turns and voltages together?
No. You only need one pair to set the ratio, either both voltages or both turns. Supplying a primary voltage or primary current then lets the tool derive the secondary values.
Does this assume an ideal transformer?
Yes. It assumes no losses, so the volt-amps on each side are equal and power is conserved. Real transformers have small copper and core losses that lower the secondary slightly.
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