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Transformer Efficiency Calculator

Online calculator for transformer efficiency at any loading factor differs from rating.

Iron Loss
Rating Copper Loss
Actual Loading

Actual Copper Loss
Total Transformer Loss
Transformer Efficiency at Loading

What is formula for efficiency

Transformer efficiency is derived from the rated output and the losses that occurred in the transformer. The basic relationship for efficiency is the output over the input, which translates to:


In normal conditions, efficiency decreases slightly with increases in load. Total losses are the sum of the no-load (iron loss) and load losses (copper loss). In addition, changing the power factor of the load does not change the losses. However, raising the load power factor will improve the efficiency of the transformer.

How is transformer efficiency calculated

Transformer efficiency at a loading factor aka actual loading is replied on rating losses and of course load consumption.

The rating losses can be derived from the transformer nameplate. Below is an example of a nameplate with losses indication. The rating losses then input to above transformer efficiency calculator to come up with specific overall efficiency.