Free Transformer Turns Ratio Calculator

Calculate primary-to-secondary turns ratio, step-up/step-down voltage conversion, current ratios, and reflected impedance matching.

⚡ Winding Voltages & Turns

Calculation Mode

Primary Voltage V_p (V) Input AC RMS voltage

Secondary Voltage V_s (V) Target output AC voltage

Primary Turns N_p

Secondary Load Current (A)

Secondary Load Z_s (Ω) e.g. 8Ω speaker load

Transformer Efficiency (%)

📊 Calculated Transformer Specs

Turns Ratio (N_p : N_s)

10.00 : 1

Step-Down Transformer (10:1 Voltage Reduction)

Secondary Turns N_s

50 Turns

Based on 500 primary turns

Primary Current I_p

0.263 A

At 95% rated efficiency

Reflected Primary Impedance (Z_p): 800.0 Ω

Apparent Power Rating: 30.0 VA (Watts)

Turns per Volt (Te/V): 4.17 Turns / Volt

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Understanding Transformer Turns Ratios

An ideal transformer transfers electrical energy between two or more circuits through electromagnetic induction. The physical ratio of wire turns in the primary winding ($N_p$) to secondary winding ($N_s$) directly governs voltage scaling, current inverse scaling, and impedance multiplication.

Fundamental Transformer Relationships

a = \frac{N_p}{N_s} = \frac{V_p}{V_s} = \frac{I_s}{I_p} \quad \text{(Turns Ratio)}

Z_p = a^2 \cdot Z_s = \left(\frac{N_p}{N_s}\right)^2 \cdot Z_s \quad \text{(Reflected Impedance)}

P_{\text{sec}} = V_s \cdot I_s \quad \longrightarrow \quad P_{\text{prim}} = \frac{P_{\text{sec}}}{\eta}

Impedance Matching in Audio & Tube Amplifiers

Vacuum tube output stages present high output impedances (typically 3,000 to 8,000 ohms), while speaker drivers require 4 or 8 ohms. Because impedance scales with the square of the turns ratio ($a^2$), an output transformer with a turns ratio of $25:1$ transforms an 8-ohm speaker into $25^2 imes 8 = 625 imes 8 = 5,000 Omega$, matching the tube plate load for maximum power transfer.

Frequently Asked Questions

Why does secondary current increase when voltage is stepped down?

By the law of conservation of energy, electrical power input must equal power output minus internal losses (P = V * I). If voltage is reduced by a factor of 10 in a step-down transformer, current must increase by roughly a factor of 10 to maintain power balance.

What is turns-per-volt and why does it matter?

Turns per volt (TPV) is determined by magnetic core cross-sectional area, AC line frequency, and maximum allowable flux density (B_max). If too few turns per volt are wound, the magnetic core saturates, drawing excessive magnetizing current and overheating the windings.

Can transformers operate on direct current (DC)?

No. Transformers require a changing magnetic flux (dPhi/dt) across the core to induce an electromotive force (EMF) into the secondary coil. Steady DC creates a static magnetic field, which induces 0 volts into the secondary and acts as a dead short-circuit on the primary.