Transformer Turns Ratio Calculator
Calculate Primary/Secondary Voltage or Coil Turns. Enter exactly three values to solve for the fourth.
Understanding Transformer Turns Ratios
A Transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits. It achieves this using electromagnetic induction. A varying current in any one coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying voltage across any other coils wound around the same core.
[Image of step-up and step-down transformer schematics]By simply changing the number of times the wire is wrapped around the core (the "Turns"), engineers can mathematically scale Alternating Current (AC) voltage up or down with incredible precision. Our Turns Ratio Calculator handles the math for you, whether you are designing an audio amplifier or analyzing national power grid transmissions.
Glossary of Transformer Variables
- Primary Voltage (Vp): The AC voltage applied to the input coil of the transformer.
- Secondary Voltage (Vs): The AC voltage produced at the output coil of the transformer.
- Primary Turns (Np): The physical count of how many times the input wire is wrapped around the magnetic core.
- Secondary Turns (Ns): The physical count of how many times the output wire is wrapped around the magnetic core.
The Universal Transformer Equation
In an ideal transformer (assuming no energy is lost to heat or magnetic leakage), the ratio of the voltages is perfectly equal to the ratio of the number of turns. This gives us our core formula:
The Turns Ratio Formula:
Vp / Vs = Np / Ns
Types of Transformers & Examples
1. Step-Down Transformers
A step-down transformer has more turns on the primary coil than the secondary coil. This reduces the voltage. These are found on utility poles outside houses, stepping down massive 7,200V power lines to the safe 120V/240V used inside your home.
Example: You have a 120V wall outlet (Vp) and you want to build a power supply for a 12V electronics project (Vs). Your primary coil has 500 turns (Np). How many turns do you need for the secondary coil (Ns)?
Formula: Ns = (Vs / Vp) × Np
Ns = (12 / 120) × 500 = 50 Turns
2. Step-Up Transformers
A step-up transformer has fewer turns on the primary coil than the secondary coil, increasing the voltage. These are used in microwave ovens, neon signs, and power plants (to push electricity across long distances with minimal power loss).
Example: You are analyzing a microwave oven. The wall provides 120V (Vp). The internal transformer has 200 primary turns (Np) and 3,500 secondary turns (Ns). What is the output voltage (Vs) going to the magnetron?
Formula: Vs = (Ns / Np) × Vp
Vs = (3,500 / 200) × 120 = 2,100 Volts
3. Isolation Transformers
If the primary and secondary coils have the exact same number of turns (a 1:1 ratio), the voltage does not change. This is called an Isolation Transformer. It is used heavily in medical equipment and test benches to physically disconnect the device from the wall grid, preventing dangerous shock hazards if a component shorts out to the chassis.