The net protein utilization ie NPU It is the ratio of Amino acids converted into proteins by amino acids supplied. This figure depends upon the presence of essential amino acids in the body but it is more affected by the level of limiting amino acids within a foodstuff.

this value can be determined by determining dietary protein intake and then measuring nitrogen excretion. One formula for NPU is:

NPU = ((0.16 × (24 hour protein intake in grams)) - ((24 hour urinary urea nitrogen) + 2) - (0.1 × (ideal body weight in kilograms))) / (0.16 × (24 hour protein intake in grams))

NPU can range from 0 to 1. 0 indicates none of the amino acids supplied to the body is not converted into protein and 1 indicated that all of amino acids supplied to the body got converted into the protein.

Certain foodstuffs, such as eggs or milk, rate as 1 on an NPU chart.

The Protein Digestibility Corrected Amino Acid Score (PDCAA) is a more modern way of rating the protein quality.