For many years, mitochondrial phosphate-to-oxygen ratios were believed to be integral values: 3 for ATP/NADH and 2 for ATP/FADH[subscript 2]. The chemiosmotic theory has demonstrated that this need not be the case because coupling sites do not directly synthesize ATP. Coupling between coupling site redox reactions and ATP synthesis occurs via proton pumping and proton flow, respectively. Most recent measurements support phosphate-to-oxygen ratios of approximately 2.5 ATP/NADH and 1.5 ATP/FADH[subscript 2]; these values match those expected from chemiosmotic calculations. Faculty members who teach metabolism are encouraged to reflect these developments in their lecture notes.