What is the turns ratio of a transformer?

The turns ratio (N1/N2) is the ratio of primary winding turns to secondary winding turns. It equals the ratio of primary voltage to secondary voltage: N1/N2 = V1/V2. A ratio greater than 1 means step-down; less than 1 means step-up.

How is reflected impedance calculated?

The impedance reflected to the primary is Z_primary = (N1/N2)² × Z_load. Squaring the turns ratio means a 2:1 step-down transformer reflects the secondary load as 4 times its value back to the primary.

What is impedance matching and why does it matter?

Maximum power transfer occurs when the source impedance equals the load impedance. A transformer transforms the effective load impedance seen by the source by the square of the turns ratio, enabling optimal power transfer between mismatched impedances.

Does this calculator assume an ideal transformer?

Yes. The formulas assume zero winding resistance, no core losses, and perfect magnetic coupling (k = 1). Real transformers introduce leakage inductance and resistive losses that reduce efficiency, especially at high frequencies.

How do I find the secondary current from these results?

Secondary current is I2 = V2 / Z_load. By conservation of power in an ideal transformer, primary current I1 = I2 × (N2/N1). Both values are shown in the results panel.

Can I use this for RF transformers?

The impedance formulas apply at any frequency for an ideal transformer. Real RF transformers have frequency-dependent behaviour (leakage, core permeability), but the turns ratio and reflected impedance calculations remain the starting point for RF matching networks.

Transformer Impedance Calculator

Enter primary and secondary voltages with a load impedance to instantly compute the turns ratio and reflected impedance.

Transformer Parameters

Primary Voltage (V₁)

Secondary Voltage (V₂)

Secondary Load Impedance (Z_load)

Source Impedance (Z_source) (optional)

Circuit Diagram

Results

Enter transformer parameters and click Calculate

Common Turns Ratios & Impedance Transformation

Ratio (N1:N2)	V1 / V2	Z Multiplier	Use Case
10 : 1	120V / 12V	100×	Mains to low-voltage DC
2 : 1	240V / 120V	4×	Step-down isolation
2 : 1	2V / 1V	4×	Audio line matching
1 : 1.732	1V / 1.732V	1/3×	RF impedance step-up

Click a row to load those values.

Summary

This transformer impedance calculator determines the turns ratio (N1/N2) from the primary and secondary voltages, then uses that ratio to compute the impedance reflected back to the primary side. Enter any load impedance on the secondary to see how it appears at the primary terminals. Supports both step-up and step-down configurations.

How it works

Enter the primary winding voltage (V1) in volts.
Enter the secondary winding voltage (V2) in volts.
Enter the load impedance on the secondary side and select its unit (Ω, kΩ, MΩ).
Optionally enter the primary source impedance to compute impedance matching efficiency.
Click Calculate to see the turns ratio, reflected impedance, and secondary current.
Review the formula breakdown and circuit diagram for design verification.

Use cases

Matching speaker or load impedance to amplifier output stages.
Designing isolation transformers for instrumentation circuits.
Verifying transformer selection in power supply schematics.
Computing reflected impedance for RF and audio transformer design.
Teaching or studying transformer theory with instant numerical feedback.
Checking impedance matching efficiency between source and load.
Designing inter-stage coupling transformers in vacuum tube amplifiers.
Scaling sensor impedances to match ADC or receiver input requirements.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu