ElectroHub

Transformer Turns Ratio Calculator

An ideal transformer trades voltage for current at constant power. The turns ratio sets the trade exactly: double the turns, double the voltage, halve the current.

Transformer

Np ÷ Ns = Vp ÷ Vs. Enter one complete pair (both turns or both voltages) and any other value; the rest are filled in.

Turns ratio a = Np/Ns
Type
Primary voltage
Secondary voltage
Primary turns
Secondary turns
  1. 1.Formulaa = Np ÷ Ns = Vp ÷ Vs (ideal transformer)Resulta = 10 (step-down)
  2. 2.FormulaVs = Vp ÷ aSubstituteVs = 230 ÷ 10ResultVs = 23 V
  3. 3.Currents invert: Is ÷ Ip = a → secondary current is 10× the primary
Common trap: A transformer steps voltage down but current up by the same ratio — power (minus losses) is conserved. And it only works on AC: put DC on the primary and you get no output, just a heater (and possibly smoke).

The formula

N_p / N_s = V_p / V_s = I_s / I_p

N_p, N_s
primary and secondary turns
V_p, V_s
primary and secondary voltages (volts)
I_p, I_s
primary and secondary currents (amperes)

Worked example

N_p = 1000 turns, N_s = 100 turns, primary at 230 V.

  1. Turns ratio a = 1000 / 100 = 10
  2. V_s = V_p / a = 230 / 10
  3. Current ratio is inverted: I_p = I_s / 10

23 V secondary — a 10:1 step-down, where 1 A drawn from the secondary reflects as 100 mA in the primary.

Where you'll use it

Picking a transformer for a power supply, understanding distribution voltages, and impedance matching in audio and RF, where impedance transforms as the square of the turns ratio. The calculator flags inconsistent inputs, since four numbers can easily describe two different transformers.

The laws behind it

Parts this applies to

Inductor / CoilTransformer (power)Current / Potential Transformer (CT/PT)DC MotorSpeaker / MicrophoneRCCB / RCD / GFCICurrent Sensor (Hall / Shunt / CT)LVDT & Displacement Transducers

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