What is a transformer turns ratio?

The turns ratio is the primary winding turns divided by the secondary winding turns. In an ideal transformer it is also equal to the primary voltage divided by the secondary voltage.

Does efficiency change the transformer turns ratio?

No. Efficiency affects real input power and losses, but the basic voltage ratio is set primarily by the winding turns ratio.

Can I use the calculator to design a mains transformer?

The tool provides electrical estimates only. Safe transformer design also requires core area, flux density, frequency, wire size, insulation, temperature rise, regulation, inrush current, protection, and applicable safety standards.

Why is measured secondary voltage different from the calculated voltage?

Real transformers have winding resistance, leakage reactance, magnetic losses, supply variation, and load regulation, so measured voltage can differ from the ideal turns-ratio result.

Electrical and Energy

Transformer Calculator

Calculate transformer voltage, winding turns, turns ratio, rated current, VA capacity, real output power, and estimated efficiency losses with clear formulas for practical electrical work.

Turns ratio VA and current 1φ and 3φ sizing

Enter transformer values

Choose the calculation that matches the information available.

How It Works

How to use the transformer calculator

Select the calculation that matches your known values. The tool applies the ideal transformer relationship for voltage and turns, or the correct apparent-power formula for single-phase and balanced three-phase transformer sizing.

Choose a calculation

Analyse a winding set, calculate missing turns, determine VA capacity, or find rated current.

Enter nameplate values

Use RMS voltage, winding turns, VA rating, current, power factor, and efficiency where requested.

Verify the design

Review the formula and confirm insulation, thermal, core, conductor, protection, and regulation requirements separately.

Transformer Guide

Transformer formulas and practical electrical guidance

A transformer transfers AC energy magnetically between windings. The winding-turn ratio sets the ideal voltage ratio, while the VA nameplate determines the approximate full-load current available at each winding.

Voltage and turns ratio

Voltage ratioVP ÷ VS = NP ÷ NS

Secondary voltageVS = VP × NS ÷ NP

Secondary turnsNS = NP × VS ÷ VP

VA and current

Single-phaseVA = V × I

Three-phase line valuesVA = √3 × VL × IL

Single-phase currentI = VA ÷ V

Efficiency and losses

Efficiency compares useful output watts with input watts. Copper loss increases with current, while core loss depends strongly on voltage, frequency, material, and flux density.

Transformer calculation reference

Calculation	Formula	Use	Important assumption
Turns ratio	NP ÷ NS	Compare primary and secondary windings	Per-winding voltage values
Secondary voltage	VP × NS ÷ NP	Estimate no-load ideal output	Ignores regulation and losses
Single-phase rated current	VA ÷ V	Estimate full-load winding current	Uses RMS voltage
Three-phase rated current	VA ÷ (√3 × VL)	Estimate balanced line current	Uses line-to-line voltage
Output real power	VA × PF	Estimate load watts	Requires load power factor
Estimated input watts	Output W ÷ efficiency	Estimate loss and input energy	Efficiency entered as an estimate

A turns-ratio calculator is not a complete transformer-design tool. Building or modifying a transformer also requires core cross-section, frequency, flux density, winding window, conductor current density, insulation system, creepage, clearance, temperature rise, short-circuit protection, inrush control, and regulatory compliance.

Frequently Asked Questions

Transformer calculator FAQs

How is transformer secondary voltage calculated?

For an ideal transformer, multiply the primary voltage by the secondary-to-primary turns ratio: VS = VP × NS ÷ NP. Use winding RMS voltages measured across the corresponding windings.

How do I calculate transformer current from VA?

For single-phase operation, divide the VA rating by winding voltage. For balanced three-phase operation using line values, divide VA by √3 times the line-to-line voltage.

What does a 10:1 transformer ratio mean?

A primary-to-secondary turns ratio of 10:1 ideally reduces voltage by a factor of ten and increases available secondary current by approximately the same factor, subject to the transformer's VA rating and losses.

Does transformer efficiency affect the voltage ratio?

Efficiency does not directly change the ideal turns-ratio equation. However, real output voltage falls under load because of winding resistance, leakage reactance, magnetic losses, and regulation.

Can I calculate a three-phase transformer with this tool?

The VA-rating and current modes support balanced three-phase line values. Turns calculations should use the voltage across the individual winding being analysed because delta and star connections change the relationship between line and phase voltage.

Why is the measured secondary voltage higher at no load?

Manufacturers may design the no-load voltage slightly high so it falls closer to the rated value at full load. Supply tolerance and the transformer's regulation percentage also influence the measurement.

High-voltage safety reminderTransformer windings can involve lethal voltage, stored energy, high fault current, and fire risk. De-energise, isolate, discharge, fuse, earth, and verify equipment according to applicable electrical standards and qualified professional practice.