What is the transformer voltage equation?

The ideal transformer equation is Vs / Vp = Ns / Np, where Vp is primary voltage, Vs is secondary voltage, Np is the number of primary turns, and Ns is the number of secondary turns. Rearranging: Vs = Vp × (Ns / Np).

What is the turns ratio?

The turns ratio (a) is Np / Ns. A turns ratio greater than 1 means step-down (output voltage is lower); less than 1 means step-up (output voltage is higher). A ratio of exactly 1 is an isolation transformer.

Does this calculator account for real-world losses?

No — this calculator uses the ideal transformer model. Real transformers have copper losses, core losses, and leakage inductance that reduce efficiency. For precision engineering, apply an efficiency factor (typically 0.95–0.99) to the result.

Can I use this for AC and DC transformers?

Standard transformers only work with AC. The voltage equation applies to AC transformers. DC cannot be transformed by a standard magnetic transformer.

What is a step-up vs. step-down transformer?

A step-up transformer has more secondary turns than primary (Ns > Np), increasing voltage. A step-down transformer has fewer secondary turns (Ns < Np), decreasing voltage. Power is conserved in both cases (ignoring losses).

Transformer Voltage Calculator

Name: Transformer Voltage Calculator
Availability: InStock
Author: Nham Vu

Enter primary voltage and turns ratio (or individual turn counts) to instantly find secondary voltage — or solve for any unknown in the transformer equation.

Transformer Inputs

Solve For

Turns Input Mode

Primary Voltage (V_p) — Volts

Turns Ratio (N_p / N_s)

Enter Np ÷ Ns. >1 = step-down, <1 = step-up, 1 = isolation.

Secondary Voltage (V_s) — Volts

Result

Fill in the inputs and click Calculate.

Transformer Equation

V_s / V_p = N_s / N_p

Step-Up

N_s > N_p → V_s > V_p

Step-Down

N_s < N_p → V_s < V_p

Isolation

N_s = N_p → V_s = V_p

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Summary

Enter primary voltage and turns ratio (or individual turn counts) to instantly find secondary voltage — or solve for any unknown in the transformer equation.

How it works

Select which value you want to solve for: secondary voltage, primary voltage, or turns ratio.
Enter the known values in the input fields.
The result updates instantly using the transformer equation Vs/Vp = Ns/Np.
Switch to "Turns Count" mode to enter the number of primary and secondary turns directly.
Use the transformer type indicator to confirm step-up, step-down, or isolation behavior.

Use cases

Verify secondary voltage when designing power supply circuits.
Find the required turns ratio to achieve a target output voltage.
Check if a transformer is step-up or step-down before installation.
Educational demonstrations of the transformer voltage equation.
Calculate primary voltage needed for a given turns ratio and output requirement.
Quick reference during electronics lab work or homework.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu