Transformer Turns Ratio Calculator
Voltage, current and turns for a transformer.
Enter your values
Enter the primary voltage in V.
Enter the secondary voltage in V.
Enter the primary turns you are working with.
Enter the secondary current in A.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Voltage, current and turns for a transformer. |
|---|---|
| Category | Engineering |
| Inputs needed | Primary voltage, Secondary voltage, Primary turns, Secondary current |
| Main output | Turns ratio |
| Formula | Vp ÷ Vs = Np ÷ Ns |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Primary voltage(V)
- Enter the primary voltage in V.
- Secondary voltage(V)
- Enter the secondary voltage in V.
- Primary turns
- Enter the primary turns you are working with.
- Secondary current(A)
- Enter the secondary current in A.
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.
What do I need to enter into the Transformer Turns Ratio Calculator?
Just 4 values: primary voltage, secondary voltage, primary turns, secondary current. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Transformer Turns Ratio Calculator work out the answer?
Transformer voltage ratio equals the turns ratio, while current ratio is its inverse. It applies the formula Vp ÷ Vs = Np ÷ Ns and shows the working so you can check each step by hand.
Is the Transformer Turns Ratio Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.