Electrical · magnetics

Transformer Calculator

Drag the turns. Watch the coils — and the physics — change together.
V₁/V₂ = N₁/N₂ = I₂/I₁
10 : 2 turns · 230V in

Windings

modify live

Supply & load

Common ratios

same behaviour

Core & windings

Efficiency vs. load

Primary & secondary, live

primary voltage secondary voltage both windings share one AC cycle — no phase shift in an ideal transformer
Field notes

Why turns ratio is the whole story — until losses show up

Using this tool

Turns ratio, then reality

An ideal transformer is defined entirely by its turns ratio: V₁/V₂ = N₁/N₂. Because power in equals power out for an ideal device, current runs the other way — I₂/I₁ = N₁/N₂ — so a step-down winding that halves the voltage doubles the current. Drag either turns slider here and every other number updates instantly, because they're all derived from that one ratio.

Worked example

230V into a 1000:100 turns transformer (a 10:1 ratio) gives 23V out. A 100W load at 23V draws 4.35A on the secondary and 0.43A on the primary — checked against ampere-turns balance, 1000 × 0.43A matches 100 × 4.35A exactly.

Why isn't a real transformer 100% efficient?

Two loss mechanisms eat into it: core (iron) losses from magnetising the core, which are present constantly whenever the transformer is energised regardless of load, and copper losses from winding resistance, which scale with the square of the load current. Distribution transformers typically run 97–99% efficient at full load; large power transformers can exceed 99.5%.

Why does the efficiency chart peak partway up, not at full load?

Efficiency is maximised exactly where copper loss equals core loss — since core loss is constant and copper loss grows with current squared, that crossover typically happens around 40–70% of rated load for distribution transformers, which is also why they're deliberately sized a little larger than their average expected load.

Why does the visual only show a handful of turns for a real 20:1 transformer?

A real mains transformer might use hundreds or thousands of turns per winding — this tool draws the turns ratio at a legible scale (the presets pick small whole numbers with the same ratio) so the physics stays identical while the diagram stays readable.

Does turns ratio alone determine everything about a transformer?

Only for the ideal case. Real transformers also have leakage inductance, magnetising current, and winding resistance that this tool's core equations don't model — turns ratio gets you the voltage and current relationship exactly right, which is most of what matters for a first-pass calculation.

Why are the two waveforms perfectly in phase, never shifted?

Because they're driven by the same changing magnetic flux in the same core at the same instant — there's no physical mechanism for an ideal transformer to delay one winding relative to the other. A phase shift would only show up from added leakage inductance or a reactive load, neither of which this ideal-transformer model includes.