Transformer secondary turns

Type U1, U2, and n1. The calculator computes n2 = n1 U2/U1: 230 V, 12 V and 1150 turns give 60, and 24 V at the same n1 gives 120. U1 must be greater than zero, because the calculator divides by it.

Voltage U2: U2 = U1 n2/n1. Induction: |ε| = ΔΦ/Δt.

Inputs

Result

Primary voltage U1 (V), Secondary voltage U2 (V) and Primary turns n1. The result shows up here.

How it works

U1, U2, n1 n2 n2 = n1·(U2/U1) n2 ← U1, U2, n1
You know both voltages and n1: you want the secondary turn count n2.

Secondary turns come from the same ratio as the voltages: n2 = n1 U2/U1, or U2/U1 = n2/n1. At 230 V, 12 V and n1 = 1150 you get n2 = 60. At 230 V, 24 V and 1150 you get 120: twice the U2, twice the turns. At 230 V, 5 V and n1 = 2300 you get n2 = 50.

Three fields: U1 and U2 in volts, n1 as a turn count. The result n2 is a turn count too, with no unit. A comma and a period in 12.5 are the same U2. The model is ideal, with no losses and no magnetizing current.

U1 must be positive. Zero does not divide. All three fields need a number before 60 can appear. If n2 comes out as a fraction, you round to a whole number of turns on the winding.

The sibling card computes U2 = U1 n2/n1 when you already know both windings. Here you know both voltages and n1, and you want n2. Same ratio, different unknown.

120 V to 12 V at n1 = 600 also gives n2 = 60. 12 V to 230 V at n1 = 60 gives n2 = 1150: you are stepping up, so the secondary has more turns. At U1 = U2 = 230 V and n1 = 800 you get n2 = 800.

Type 230, 12 and 1150, click Calculate, and match 60. Then change U2 to 24 and see 120. Ohm and power P = U I are separate cards once you already have U2.

How to use

  1. In the first field enter primary voltage U1 in volts, for example 230. In the second enter secondary voltage U2, for example 12.
  2. In the third field enter the primary turn count n1, for example 1150.
  3. Click Calculate. The calculator computes n2 = n1 U2/U1. 230 V, 12 V and 1150 give n2 = 60.
  4. U1 must be positive. Zero does not divide. All three fields need a number.
  5. Want U2 from known turns? Open the transformer page U2 = U1 n2/n1. Here it stays n2.

Formula

n2 = n1 · (U2 / U1)

U1 > 0, U2 > 0, n1 > 0.

Turns n2 from a voltage pair

Same ratio, different unknown: n2 = n1·U2/U1. 230 V to 12 V at 1150 turns gives n2 = 60. To 24 V you get 120.

n2
The unknown secondary turns. 1150 × 12 / 230 = 60. Round a fraction on the winding.
n1
Known primary turns, for example 1150. When U1 = U2 you get n2 = n1.
U2
Wanted secondary voltage. 12 V or 24 V. Double U2, double n2.
U1
Primary voltage. 230 V. U1 = 0 does not divide.

Real-life examples

Example 1

U1 = 230 V, U2 = 12 V, n1 = 1150 -> n2 = 60.

Example 2

U1 = 230 V, U2 = 5 V, n1 = 2300 -> n2 = 50.

Example 3

U1 = 230 V, U2 = 24 V, n1 = 1150 -> n2 = 120.

Example 4

U1 = 120 V, U2 = 12 V, n1 = 600 -> n2 = 60.

Example 5

U1 = 12 V, U2 = 230 V, n1 = 60 -> n2 = 1150.

Example 6

U1 = U2 = 230 V, n1 = 800 -> n2 = 800.

Example 7

U1 = 400 V, U2 = 230 V, n1 = 800 -> n2 = 460.

Example 8

U1 = 230 V, U2 = 12 V, n1 = 920 -> n2 = 48.

Ways to use this calculator

  • You pick 60 turns for 12 V from 1150 on 230 V.
  • At 24 V with the same n1 you get 120 turns.

Related calculators

Power P = U·I
The nameplate lists volts; current is a separate step
Ohm's law
Winding voltage from Ohm, once you already have U2.
Transformer calculator U2 = U1·(n2/n1)
Secondary voltage of an ideal transformer
Faraday induction
Induced EMF from how fast the magnetic flux is changing.
Inductive reactance calculator XL = 2πfL
Coil reactance grows with frequency and inductance.
Capacitive reactance calculator Xc = 1/(2πfC)
Capacitor reactance falls as frequency or C grows.

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Frequently asked questions

How much n2 at 230 V, 12 V and n1 = 1150?

n2 = 1150 × 12 / 230 = 60. At 230 V, 24 V and 1150 you get 120.

Which units do I type?

U1 and U2 in volts, n1 is a turn count. n2 is turns too, with no unit.

What if U1 = 0?

Zero does not divide. U1, U2 and n1 must be positive. All three fields need a number.

How is this different from U2 = U1 n2/n1?

Here you want n2. There you want U2. Same ratio U2/U1 = n2/n1.

Can n2 come out as a fraction?

It can. On a winding you round to a whole number of turns.

Does a comma in 12.5 V work?

Yes. 12,5 and 12.5 mean the same U2 [V]. Then n2 = n1 × (U2/U1).

Does the calculator include losses?

Ideal model. Efficiency η = P_out / P_in lives on its own page.

How much at 120 V, 12 V and n1 = 600?

n2 = 60. At 12 V, 230 V and n1 = 60 you get n2 = 1150.

How much at U1 = U2 = 230 V and n1 = 800?

n2 = 800. The ratio is 1, so the secondary has the same turn count.

Where are Ohm and power?

U = I R and P = U I are separate cards. Here only turns from a voltage pair.

Knowledge sources

The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.

Page updated in 2026.