What a Transformer Calculator Solves

A transformer moves electrical energy between two circuits that share a magnetic core. Because the two windings never touch, the only quantities that link them are the number of turns on each coil (Np and Ns) and the magnetic flux they both see. That gives three simple relationships for an ideal transformer: the voltage ratio equals the turns ratio (Vp / Vs = Np / Ns), the current ratio is its inverse (Ip / Is = Ns / Np), and apparent power is preserved on both sides (Vp × Ip ≈ Vs × Is).

This calculator applies those relationships to your winding data and reports the derived quantity, the turns ratio, the winding-by-winding breakdown, the reflected impedance, and an efficiency estimate built from your copper and core losses. Choose whether you want the secondary voltage, the secondary current, or the secondary turns solved, enter the known values, and press Calculate.

How to Use the Results

The headline number is the value produced by your selected solve mode. Under it, the turns ratio and transformer type tell you at a glance whether you are stepping voltage up, stepping it down, or building an isolation transformer. A 1000:100 winding pair is a 10:1 step-down transformer, so 240 V on the primary becomes 24 V on the secondary while 2 A of primary current becomes 20 A of secondary current.

The breakdown table compares both windings side by side. Voltage and current should trade off inversely, and the apparent power figures should match closely — when they do not, the difference comes from the losses you entered in Advanced Options. The reflected secondary impedance row is the secondary impedance as seen through the ratio (Zs × ratio²), which is the number to use when matching loads and sources.

Summary Statistics collects the load-facing figures: primary and secondary apparent power, real and reactive power at your chosen power factor, copper and core loss, estimated efficiency, and how far your typed-in value sits from the solved one. That last figure is useful for sanity checking a nameplate: a large gap usually means a mistyped turn count or a winding pair that does not match the rated ratio.

Practical Notes and Limits of the Ideal Model

Real transformers lose energy three ways: copper loss from winding resistance (I²R), hysteresis loss as the core material resists magnetisation changes, and eddy-current loss circulating inside the core laminations. Large distribution transformers still exceed 98% efficiency because those losses are small relative to the power they carry, while small signal transformers often sit below 90%. The Advanced Options let you express copper loss as a percentage of apparent power and core loss as a fixed number of watts, which is enough to produce a realistic efficiency estimate without a full magnetics simulation.

The model assumes sinusoidal excitation at the frequency the transformer was rated for, no saturation, no leakage flux between windings, and a load described by a single power factor. Those assumptions are standard for first-pass design work and for checking whether an existing transformer is suited to a new voltage level. For high-frequency switching magnetics, saturable reactors, or anything running near core saturation, treat the results as a starting point and verify against the manufacturer's data sheet, because leakage inductance and winding capacitance begin to dominate at those extremes.