# Transformer Calculator

Calculate transformer turns ratio, secondary voltage, secondary turns, and current ratio. Free online transformer calculator for ideal transformers.

## What this calculates

A transformer converts AC voltage between different levels using electromagnetic induction between two coils. The fundamental relationship is V1/V2 = N1/N2, where V is voltage and N is the number of turns. This calculator determines turns ratio, secondary turns, and current relationships for an ideal transformer.

## Inputs

- **Primary Voltage** (V) — min 0 — Voltage applied to the primary winding.
- **Secondary Voltage** (V) — min 0 — Desired output voltage on the secondary winding.
- **Primary Turns** — min 1 — Number of turns on the primary coil.
- **Primary Current (optional)** (A) — min 0 — Current in the primary winding (for power calculation).

## Outputs

- **Turns Ratio (N1:N2)** — Ratio of primary to secondary turns.
- **Secondary Turns** — Number of turns needed on the secondary coil.
- **Current Ratio (I2/I1)** — Secondary current is multiplied by this factor relative to primary.
- **Secondary Current** (A) — Current in the secondary winding (if primary current is provided).
- **Power (VA)** (VA) — Apparent power transferred (ideal transformer).

## Details

An ideal transformer transfers power from the primary to the secondary winding with no losses. The voltage ratio equals the turns ratio: V1/V2 = N1/N2. A step-down transformer has more primary turns than secondary, reducing voltage; a step-up transformer has fewer primary turns, increasing voltage.

Since power is conserved in an ideal transformer (P1 = P2), the current ratio is the inverse of the voltage ratio: I2/I1 = N1/N2 = V1/V2. Stepping down voltage steps up current proportionally, and vice versa.

Real transformers have losses from copper resistance (I²R heating), core losses (hysteresis and eddy currents), and leakage flux. Efficiency of well-designed power transformers typically ranges from 95% to 99%. Transformers are essential for the electrical grid, converting high-voltage transmission to lower distribution voltages.

## Frequently Asked Questions

**Q: What is a transformer turns ratio?**

A: The turns ratio is N1/N2, the ratio of primary coil turns to secondary coil turns. It equals the voltage ratio V1/V2 and determines whether the transformer steps voltage up or down.

**Q: Can a transformer change DC voltage?**

A: No. Transformers require a changing magnetic field, which only AC provides. DC produces a constant field with no induced voltage in the secondary. DC-DC conversion requires switching converters.

**Q: Why does stepping down voltage increase current?**

A: Power must be conserved (P = VI). If voltage decreases, current must increase proportionally to maintain the same power level. This is why high-voltage transmission uses thin wires, since the current is low.

**Q: What is the efficiency of a real transformer?**

A: Large power transformers achieve 97-99.5% efficiency. Smaller transformers (e.g., wall adapters) may only be 80-95% efficient due to proportionally larger core and copper losses.

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Source: https://vastcalc.com/calculators/technology/transformer
Category: Technology
Last updated: 2026-04-21