Transformer Current Calculator

Before entering values

Use voltage and current values from the same side of the transformer or converter. Write down whether each entry is measured, rated, assumed, or calculated.

Confirm decimal placement whenever a source uses a different unit scale. Another relevant worksheet is Current Transformer Reading Calculator.

Primary current

Default example: 2 A. Enter primary current in A.

Voltage ratio Vp/Vs

Default example: 10. Enter voltage ratio Vp/Vs.

Before accepting the number

Unit-prefix mistakes often dominate the arithmetic error.

Recheck decimal placement and unit conversion when the answer looks unusual.

How the result is calculated

The displayed result follows Is = Ip × Vp/Vs. Only Primary current and Voltage ratio Vp/Vs enter the numerical result.

Using the loaded examples gives 20.00 A. Your saved case should identify where each entry came from.

Calculate secondary current from primary current and voltage ratio Vp/Vs. For the companion primary current calculation, open Current Transformer Ratio Calculator.

How to use the result

Use Secondary current as one quantified check within the larger decision. Compare it with component ratings and isolation requirements.

Store the measurement state and conversion notes with the answer. If you also need secondary voltage, continue with Transformer Turns Ratio Calculator.

Compare two operating cases

Change Primary current from 2 A to 2.4 A with every other entry unchanged. The result changes from 20.00 A to 24.00 A.

Do not average the two cases if either could define an operating limit.

Practical limits

The ideal relationship excludes loss.

Outside the entered variables, consider leakage inductance, parasitic capacitance, saturation, switching transients, and cooling. Do not hide omitted behavior inside an unexplained correction factor.

Use voltage and current values from the same side of the transformer or converter. For CT burden, use Current Transformer Burden Calculator.

Trace the result back to its source

Review voltage ratio Vp/Vs and the remaining entries as one case. If one value belongs to another temperature, load, or time period, separate the scenarios.

The displayed secondary current should be checked against component ratings and isolation requirements. Investigate an unexpected magnitude before changing the model or adding margin.

Document any effect handled outside this page, especially isolation, creepage, waveform shape, and manufacturer operating limits. That note prevents a later reader from assuming the simple equation covered it.

Before relying on the answer