Protein Quality (PDCAAS) Calculator

About this calculator

The PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is the method the FAO and WHO proposed in 1991 and the FDA later adopted for food labeling to rate protein quality. It is calculated as the amino acid score of the protein’s limiting essential amino acid — the milligrams of that amino acid per gram of test protein divided by the milligrams found in a gram of a reference protein pattern — multiplied by the protein’s true or fecal digestibility percentage, with the final score capped at 1.0 even if the raw calculation exceeds it.

Food scientists, dietitians, and supplement manufacturers use PDCAAS to compare protein sources on a standardized scale: whey and egg protein typically score at or near the 1.0 cap, soy protein isolate scores around 0.91, and grain proteins like wheat gluten score much lower because lysine is their limiting amino acid and is only partially digestible.

This calculator takes the limiting amino acid content relative to the reference pattern and the protein’s digestibility percentage and returns the resulting PDCAAS value, letting you rate any protein source on the same scale used in nutrition labeling.