Transformer Sizing Calculator

Created by Luciano Mino
Last updated: Sep 05, 2022

Our transformer size calculator can find the right transformer size (single or three-phase) for any load you require!

Within this short text, you will learn:

  • The working principle of transformers;
  • How to size a single-phase transformer;
  • How to calculate transformer size for a three-phase transformer; and
  • More!

Keep reading to learn about all the features of this transformer kVA calculator.

How do transformers work?

Transformers are electrical devices that transform voltages. They can bring the voltage up or down depending on their purpose.

Transformers work in the following way:

  1. Alternating current (AC) flows through a coil of wire, producing a changing magnetic field.
  2. A magnetic core leads this magnetic flux through another coil of wire which has a different number of turns than our first coil.
  3. Electromagnetic induction produces an electromotive force, a voltage difference, on the second coil.
  4. According to the number of turns, this transformer will create a step-up or step-down in voltage.

How to size a transformer

We size transformers based on the load they should power and use kVA, kilo volt-ampere, to rate them (what is kVA?). A higher transformer's kVA means a higher current and voltage output.

To find the appropriate size for our load, we need two things:

  • II, the current of our load; and
  • VV our load's voltage requirement.

Then, all we need to do is plug these parameters into the respective transformer formula.

For a single-phase transformer, we have:

kVA=IV1000\text{kVA}= \frac{I\cdot V}{1000}

and for a three-phase transformer:

kVA=IV31000\text{kVA} = \frac{I\cdot V\cdot \sqrt{3}}{1000}

🙋 This transformer sizing calculator operates with both equations: it works as a single-phase transformer kVA calculator and as a 3-phase transformer calculator! Simply select the transformer type at the top of this tool and type in your parameters.

How to use our transformer sizing calculator

Using this tool is straightforward:

  1. Select the type of transformer (single or three-phase).
  2. Input your load's current requirement.
  3. Input your load's voltage requirement.
  4. Our calculator will automatically output the minimum kVA rating for the transformer. Give it a try!
Luciano Mino
Transformer type
Load current (I)
Load voltage (V)
Minimum kVA required
You can include spare capacity with the advanced mode!
People also viewed…


Use the capacitance calculator to find this physical quantity for a pair of plates from the plate area and separation and the dielectric constant (relative static permittivity) of the medium between them.

Capacitive reactance

Use our capacitive reactance calculator to find the capacitive reactance of a capacitor in an AC circuit.

Schwarzschild radius

Discover the fundamental of black hole physics with our Schwarzschild radius calculator.
main background