An aspect of protein nutrition that has not been resolved in a satisfactory manner is the utilizable energy equivalence of proteins. The existing methods overestimate the utilizable energy of proteins. A more accurate method of calculating the utilizable energy of proteins is to calculate the moles of adenosine triphosphate formed during the complete oxidation of a given amount of protein. The moles of adenosine triphosphate formed can be calculated from knowledge of the amino acid composition and knowledge of the metabolic pathway for each amino acid. A computer program is described that provides the bookkeeping required for these calculations. The available energy of a protein is calculated in this computer-based method by adjusting the energy value of the protein so that it is equivalent to that of carbohydrates and fats in providing the energy for adenosine triphosphate formation. The computer-based method was used to calculate the available energy of a group of proteins of known amino acid composition. The available energy varied from 3.02 kcal/g for collagen to 3.72 kcal/g for the protein of raw cow's milk.