About the Transformer Turns Ratio Calculator
A transformer changes one alternating voltage into another using two coils that share a magnetic core. The ratio of turns in the two coils sets the ratio of the voltages. This calculator takes the primary voltage and the number of turns on each side and gives the turns ratio, the secondary voltage, whether the transformer steps up or down, and, with the primary current, the ideal secondary current and the power. Type the primary voltage, the primary and secondary turns and, optionally, the primary current and the secondary voltage appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Transformer Turns Ratio Calculator
- 1Enter the primary voltage, the primary and secondary turns and, optionally, the primary current.
- 2Pick the units or options from the menus if the secondary voltage tool offers them.
- 3Read the secondary voltage in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the secondary voltage
Students use the formula in physics lessons, and makers use it to check a small transformer before they buy it. Engineers use turns ratios to design power supplies, isolation transformers and the signal transformers in audio and radio equipment.
Voltage and current move in opposite directions: when the voltage is stepped down, the current available goes up by the same factor. That is how a small charger turns a thin mains current into a larger low-voltage current.
How the secondary voltage is worked out
Turns ratio = primary turns ÷ secondary turns. Secondary voltage = primary voltage ÷ turns ratio. Secondary current = primary current × turns ratio (ideal, no losses). A transformer with 1,000 turns on the primary and 50 on the secondary has a ratio of 20 : 1. On 230 V it gives 11.5 V. If the primary draws 0.5 A, the secondary can supply 10 A, and the power in both is 115 W. Reversed, a 100-turn primary and 1,000-turn secondary at 12 V gives 120 V.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Secondary voltage
- Step-up or step-down
- Ideal current and power
Mistakes to avoid with secondary voltage
Real transformers lose a few percent as heat in the winding and the core, so the secondary voltage falls a little under load and the current is slightly lower than the ideal figure. They work only with alternating current: a steady DC does not induce a secondary voltage.
On phone and computer
On a phone, type into the boxes one after another and read the secondary voltage underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the secondary voltage move. The transformer turns ratio calculator works the same on both. A turns ratio sets voltage, and the load matters too. Test the circuit with the Ohm's Law Calculator, size the rating with the kVA to kW Calculator, and check the Power Factor Calculator for real power.
Features
- Voltage and current trade off
- Real units lose a few percent
- AC only
- Clear messages when the secondary voltage inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate secondary voltage?
Turns ratio = primary turns ÷ secondary turns. Secondary voltage = primary voltage ÷ turns ratio. Secondary current = primary current × turns ratio (ideal, no losses). A transformer with 1,000 turns on the primary and 50 on the secondary has a ratio of 20 : 1. On 230 V it gives 11.5 V. If the primary draws 0.5 A, the secondary can supply 10 A, and the power in both is 115 W. Reversed, a 100-turn primary and 1,000-turn secondary at 12 V gives 120 V.
What is the formula for secondary voltage?
Turns ratio = primary turns ÷ secondary turns. Secondary voltage = primary voltage ÷ turns ratio. Secondary current = primary current × turns ratio (ideal, no losses). The transformer turns ratio calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is the turns ratio?
The primary turns divided by the secondary turns. A ratio above 1 steps the voltage down.
Does a transformer create power?
No. In an ideal transformer, power in equals power out. A real one loses a few percent.
Can a transformer work on DC?
No. It needs a changing magnetic field, so only AC works.
Is this transformer turns ratio calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.