Transformer Current Calculator

Model ideal transformers and practical losses with ease. Switch methods: ratio, VA, or watts quickly. Tune inputs, compare scenarios, and download clean reports today.

Inputs

Calculation mode

Pick the method that matches your known data.

Primary voltage Vp (V)

Secondary voltage Vs (V)

Efficiency η (%)

Use 100 for ideal behavior.

Ratio Mode Options

Ratio type

Known current side

Provide one current; the other is computed.

Primary turns Np

Secondary turns Ns

Primary current Ip (A)

Secondary current Is (A)

Power-Based Options

Apparent power S (VA)

Used in VA mode. Optional in watts mode.

Real power P (W)

Power factor (0–1)

Power/VA reference side

Clarifies where S or P applies.

Notes (optional)

Reset Results appear above this form after calculation.

Formula Used

This tool assumes the standard transformer relationships and optionally includes efficiency.

Ratio: a = Np/Ns and ideally a = Vp/Vs
Current ratio (ideal): Ip/Is = Ns/Np, so Is = Ip·(Np/Ns)
Power (approx.): S ≈ V·I where S is in VA
Efficiency: Pout = η·Pin, used to estimate current draw
With voltages and η: Ip ≈ (Vs·Is)/(Vp·η) and Is ≈ (Vp·Ip·η)/Vs

For non-linear loads, harmonics, and regulation, treat results as first-order estimates.

How to Use This Calculator

Select a calculation mode that matches what you know.
Enter Vp and Vs whenever available for best accuracy.
For ratio mode, choose turns or voltages, then input one current.
For VA mode, enter S and voltages to get both currents.
For watts mode, enter P and pf, then voltages.
Press Calculate; results appear above the form.
Use the CSV and PDF buttons inside the results box.

Example Data Table

Vp (V)	Vs (V)	Load S (VA)	η (%)	Ip (A)	Is (A)
230	12	180	92	0.850	15.000
120	24	480	95	4.211	20.000
400	200	10000	97	25.773	50.000

Example currents use Ip = S/(Vp·η) and Is = S/Vs.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.