# Transformer Calculator

> Calculate transformer step by step: Vs ÷ Vp = Ns ÷ Np, and for an ideal transformer Ip ÷ Is = Ns ÷ Np.

Page: https://freecalculator.tech/tools/transformer-calculator
Last reviewed: 2026-11-03

## Formula

Vs ÷ Vp = Ns ÷ Np, and for an ideal transformer Ip ÷ Is = Ns ÷ Np.

- Ideal transformer: no copper, core or leakage losses.
- Turns must be above zero.
- Power in equals power out in the ideal case.
- Vs ÷ Vp = Ns ÷ Np, and for an ideal transformer Ip ÷ Is = Ns ÷ Np.
- Inputs used: Primary voltage, Primary turns, Secondary turns, Secondary load current (optional).

## Inputs

- Primary voltage
- Primary turns
- Secondary turns
- Secondary load current (optional)

## Worked example: 230 V, 1000:52 turns

Step-down transformer.
1. Ratio = 1000 ÷ 52 = 19.23.
2. Vs = 230 ÷ 19.23 = 11.96 V.

## Common questions

### Why is the real output voltage different?

Real transformers have winding resistance and leakage, so voltage sags under load. Nameplate ratings are usually quoted at full load.

### Does a transformer work on DC?

No. It needs a changing current to induce voltage in the secondary.

### How is current affected?

Current changes in the opposite direction to voltage: stepping voltage down steps current up by the same ratio.

### How do I use the Transformer Calculator?

Enter the required values for Primary voltage, Primary turns, Secondary turns, Secondary load current (optional). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Transformer Calculator use?

Vs ÷ Vp = Ns ÷ Np, and for an ideal transformer Ip ÷ Is = Ns ÷ Np. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

### Can the Transformer Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Ideal, lossless model.
- Does not check core saturation or VA rating.
- Single-phase ratio only.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this transformer calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- OpenStax (Rice University) — https://openstax.org/details/books/university-physics-volume-2

## Cite this page

- APA: Free Calculator. (2026, November 3). Transformer Calculator. https://freecalculator.tech/tools/transformer-calculator
- MLA: "Transformer Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/transformer-calculator.
- Link: Transformer Calculator — Free Calculator, https://freecalculator.tech/tools/transformer-calculator