Transformer Turns Ratio Calculator
Voltage, current and turns for a transformer.
Enter your values
ⓘ Live results
Results
- Turns ratio
- 20:1
- Secondary turns
- 40
- Primary current
- 0.15 A
- Power
- 36 VA
Quick answer
Transformer voltage ratio equals the turns ratio, while current ratio is its inverse.
Vp ÷ Vs = Np ÷ Ns
How to use the Transformer Turns Ratio Calculator
- 1Enter primary and secondary voltages.
- 2Enter the primary turns count.
- 3Enter secondary current for the power figure.
Worked example
Using the values the calculator loads with:
Inputs
- Primary voltage240 V
- Secondary voltage12 V
- Primary turns800
- Secondary current3 A
Results
- Turns ratio20:1
- Secondary turns40
- Primary current0.15 A
- Power36 VA
Frequently asked questions
Are real transformers lossless?
No — expect 90–97% efficiency, so primary current is slightly higher.
Can it step up?
Yes — set secondary voltage above primary for a step-up ratio.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.