How to Figure KVA of a Transformer: Transformer KVA Calculator

A transformer is used to change the voltage level of voltage. The transformers are of two types, step-up and step-down transformers. A transformer can be selected based on the following parameters a) Power rating (kVA) b) Primary Voltage (Vp) c) Secondary Voltage (Vs) and d) Tapping arrangement. Learn how to figure out the KVA of a transformer by using the online Transformer KVA Calculator.

Transformer KVA Calculator

Put the type of transformer, power rating in KVA, Voltage in volts, and Current in amperes to calculate the other parameters. Put only two parameters to calculate the third parameter and select the type of transformer.

Transformer Type

Power Rating, (kVA)

Voltage, V(v)

Current, I(amp)

The KVA calculation is based on the voltage and amperage of the transformer. The KVA of the transformer is the same primary and secondary sides. The single-phase transformer KVA calculation can be as the following formula.

$KVA = V \times I $

For a three-phase transformer, the KVA calculation can be as the following formula.

$KVA = \frac{\sqrt{3}\times V \times I}{1000}$

Where V is the voltage, and I is the current of the transformer.

Transformer KVA calculator
Short Answer Questions:

Why Transformer Rating is in KVA Not in KW?

Manufacture design and produce a transformer for a specific range of current and voltage. And that specific range of voltage and current may produce certain losses in the transformer. When a different load is connected to the transformer it may work on different power factors.

Transformer ratings are specified in kilovolt-amperes (kVA) because they handle both real and reactive power. The apparent power (kVA) in contract to active power (KW) considers these components, ensuring proper capacity for diverse loads.

How to calculate the KVA rating of a transformer?

To calculate the kilovolt-ampere (kVA) rating of a transformer, you can use the formula:

For single phase transformer:

$ kVA = \frac{V \times I}{1000} $


  • $ kVA $ is the transformer rating in kilovolt-amperes,
  • $ V $ is the voltage in volts, and
  • $ I $ is the current in amperes.

This formula is applicable for single-phase transformers.

For three-phase transformer:

$kVA = \frac{\sqrt{3} \times V_{\text{line}} \times I_{\text{line}}}{1000} $


  • $V_{\text{line}} $ is the line-to-line voltage in volts, and
  • $ I_{\text{line}} $ is the line current in amperes.

Ensure that the voltage and current values used in the calculation are the effective (rms) values.

For a more accurate assessment, power factor correction may be necessary, especially in situations where the load has a significant reactive power component.

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