When the AC source voltage and the load voltage differ, transformers are used to increase or decrease the voltage levels. When sizing or selecting a transformer for a certain application, the calculation of kVA rating is important. A basic transformer kVA calculator is provided below to determine appropriate required kVA rating of a transformer for an applied load.

The capacity of a transformer, measured in kVA, is determined by the load voltage and the load current.

**Formula:**

In order to determine the kVA, it is necessary to know both the line-to-line voltage (V) requirement of the load as well as the maximum load phase current (I).

**In the case of a transformer with a single phase:**

**kVA = (V x I) /1000**

**In the case of a transformer with a three phase:**

**kVA = (âˆš3 x V x I) /1000**

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