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Transformer Calculator

This transformer calculator works from the primary voltage and the turns: at 230 V and 1,000 to 52 turns the secondary voltage is 11.96 V. It also shows the turns ratio, the currents and the loss.

Example: What are you looking for: Secondary voltage U₂ · Primary voltage U₁ 230 V · Primary turns N₁ 1,000 · Secondary turns N₂ 52 · Secondary load current I₂ 5 A · Efficiency 95 % → Result: Secondary voltage U₂ = 11.96 V. Source: Wikipedia – Transformator (Übersetzungsverhältnis, Ersatzschaltbild). Updated: .

V
A
%
Small mains transformers 80 to 95 %, large ones above 98 %
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Result

Result
Secondary voltage U₂ = 11.96 V
Calculation values
ItemValue
Turns ratio N₁ : N₂19.231
Primary voltage U₁230 V
Secondary voltage U₂11.96 V
Primary turns N₁1,000
Secondary turns N₂52
Turns per volt (primary side)4.348
Primary current I₁0.27368 A
Secondary current I₂5 A
Input power P₁62.947 W
Output power P₂59.8 W
Power loss3.1474 W
The calculation uses the lossless voltage ratio and a flat efficiency for the currents. No-load current, leakage and load drop are not included; design and fusing belong in the hands of a qualified electrician.

How it is calculated

In an ideal transformer the voltages are in the same ratio as the turns: U₁ : U₂ = N₁ : N₂. The ratio N₁ / N₂ is the turns ratio. The currents behave the other way round, I₁ : I₂ = N₂ : N₁, because the power stays the same apart from the loss.

How it is calculated

The secondary voltage is U₂ = U₁ · N₂ / N₁. At 230 V and 1,000 : 52 turns that is 11.96 V. Conversely, a secondary voltage of 12 V with 1,000 primary turns and 230 V needs exactly 52.17 turns, rounded 52. With the load current I₂ the output power is P₂ = U₂ · I₂, the input power is P₁ = P₂ / η and the primary current I₁ = P₁ / U₁. The difference is the power loss, which turns into heat in the core and windings.

Practical notes

The value “turns per volt” depends on the core cross-section and core quality and decides whether the core saturates. Mains transformers on small cores often have 4 to 8 turns per volt. The exact design of a transformer is best left to the manufacturer.

Frequently asked questions

How do you calculate the secondary voltage of a transformer?

U₂ = U₁ · N₂ / N₁. With 230 V, 1,000 primary and 52 secondary turns that is 11.96 V.

How do you calculate the primary current?

From the secondary power: I₁ = U₂ · I₂ / (η · U₁). At 12 V, 5 A, η = 95 % and 230 V about 0.27 A flow.

What does the turns ratio mean?

N₁ / N₂ tells by what factor the voltage is stepped down (ratio above 1) or up (below 1). The current changes in the opposite ratio.

Sources and legal basis

As of: · Editorial policy

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