Transformer Calculator Formula

Understand the math behind the transformer calculator. Each variable explained with a worked example.

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Formulas Used

Turns Ratio (N2/N1)

turns_ratio = n2 / n1

Secondary Voltage

v2 = v1 * n2 / n1

Secondary Current

i2 = i1 * n1 / n2

Variables

VariableDescriptionDefault
v1Primary Voltage(V)120
n1Primary Turns500
n2Secondary Turns50
i1Primary Current(A)1

How It Works

Transformer

A transformer transfers electrical energy between circuits via magnetic coupling, changing voltage and current levels.

Formulas

V2 / V1 = N2 / N1 (voltage ratio equals turns ratio)

I2 / I1 = N1 / N2 (current ratio is inverse of turns ratio)

Power is conserved in an ideal transformer: P1 = P2.

Worked Example

A step-down transformer: 120 V input, 500 primary turns, 50 secondary turns, 1 A primary current.

v1 = 120n1 = 500n2 = 50i1 = 1
  1. 01Turns ratio = N2/N1 = 50/500 = 0.1
  2. 02V2 = V1 * N2/N1 = 120 * 0.1 = 12 V
  3. 03I2 = I1 * N1/N2 = 1 * 500/50 = 10 A
  4. 04Power check: 120*1 = 12*10 = 120 W

Frequently Asked Questions

Can a transformer work with DC?

No. Transformers require a changing magnetic field to operate, which means they only work with AC (alternating current).

What is a step-down transformer?

A transformer with fewer secondary turns than primary, producing a lower output voltage. A step-up transformer does the opposite.

Why are transformers not 100% efficient?

Real transformers have losses from wire resistance (copper losses), magnetic hysteresis, and eddy currents in the core (iron losses).

Learn More

Guide

How to Calculate Transformer Ratios

Learn how to calculate transformer turns ratio, voltage ratio, current ratio, and impedance transformation. Includes step-up, step-down, and isolation transformer examples.

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