Ideal Transformer Calculator

Calculate secondary voltage or current from primary values and winding turns.

Calculate ideal transformer ratios

Choose a voltage or current calculation and enter the primary value plus both winding counts.

Calculation Type

Primary Voltage (V)

Primary Turns

Secondary Turns

About ideal transformers

An ideal transformer transfers alternating-current power between two windings through a changing magnetic field. The primary winding receives the source voltage, and the secondary winding delivers a transformed voltage to the load. In the ideal model, winding resistance, magnetic leakage, core loss, and magnetizing current are neglected. Those assumptions make the voltage, current, and turns relationships especially clear. Voltage follows the turns ratio. Secondary voltage divided by primary voltage equals secondary turns divided by primary turns. A secondary winding with fewer turns produces a lower voltage and is called step-down. A secondary with more turns produces a higher voltage and is called step-up. The calculator defines its displayed turns ratio as secondary turns divided by primary turns, so secondary voltage equals primary voltage multiplied by that ratio. Current changes in the opposite direction. Because an ideal transformer conserves apparent power, primary voltage multiplied by primary current equals secondary voltage multiplied by secondary current. Secondary current therefore equals primary current multiplied by primary turns divided by secondary turns. A step-down transformer reduces voltage while increasing available current, whereas a step-up transformer raises voltage while reducing current. The calculator offers separate voltage and current modes to make that inverse relationship explicit. Turns are winding counts rather than a unit of length. Only their ratio controls the ideal transformation, so 100 primary turns and 20 secondary turns produce the same ratio as 1,000 and 200. Actual designs still need enough turns for the selected core area, frequency, and flux density. Too few turns can saturate the core and cause excessive current even when the ratio appears correct. Real transformers always depart from the ideal model. Copper resistance causes winding loss and voltage drop, core hysteresis and eddy currents create heat, leakage inductance affects regulation, and no-load magnetizing current is required to establish flux. Efficiency is high for many power transformers but never exactly 100 percent. Rated voltage, frequency, insulation, temperature rise, regulation, and load power must all be considered in practical selection. Use this calculator for ratio analysis, educational problems, quick winding comparisons, and first-pass circuit estimates. It does not determine wire gauge, core size, flux density, efficiency, or safe power rating. Work involving mains or high voltage requires suitable isolation, overcurrent protection, approved components, and qualified design review. The numerical relationship is simple, but transformer construction and electrical safety are not.

Ideal transformer examples

The examples demonstrate step-down, step-up, and inverse current behavior.

Inputs	Result	Interpretation
120 V, 1000 primary turns, 100 secondary turns	12 V secondary	A 0.1 turns ratio creates a ten-to-one voltage step-down.
12 V, 100 primary turns, 1000 secondary turns	120 V secondary	A turns ratio of 10 creates a voltage step-up.
2 A, 100 primary turns, 500 secondary turns	0.4 A secondary	Current falls by the inverse of the five-to-one turns ratio.

How to use the transformer calculator

Choose Secondary Voltage or Secondary Current as the calculation type.
Enter the matching primary voltage or primary current.
Enter positive primary and secondary winding turn counts.
Select Calculate Transformer to see the secondary value and turns ratio.

Ideal transformer FAQ

What is the transformer turns ratio?

This calculator defines it as secondary turns divided by primary turns. The same ratio equals secondary voltage divided by primary voltage in an ideal transformer.

Why is the current ratio inverted?

An ideal transformer conserves input and output apparent power. Raising voltage therefore lowers current by the reciprocal ratio, and lowering voltage raises current.

Does a transformer work with direct current?

A conventional transformer requires changing magnetic flux and therefore an alternating or switched waveform. Steady direct current does not continuously induce secondary voltage and can overheat a winding.

Are real transformer outputs exactly equal to this result?

No, winding resistance, leakage, magnetizing current, and core losses change actual voltage and current. The ideal result is a useful baseline rather than a complete performance prediction.

Can this calculator determine transformer power rating?

No, power rating also depends on core size, wire gauge, temperature rise, frequency, insulation, and cooling. Use manufacturer data or a full electromagnetic design for safe hardware.