Protein efficiency ratio (PER) is based on the weight gain of a test subject divided by its intake of a particular food protein during the test period.

From 1919 until very recently, the PER had been a widely used method for evaluating the quality of protein in food.

In the United States, the food industry had long used the PER as the standard for evaluating the protein quality of food proteins. The U.S. Food and Drug Administration used the PER as the basis for the percent of the U.S. recommended daily allowance (USRDA) for protein shown on food labels.