The overall efficiency of respiration is approximately

There are two types of cellular respiration; anaerobic respiration and aerobic respiration. In anaerobic respiration 2 ATP (adenosine triphosphate; the cell's main unit of energy) per molecule of glucose is produced via glycolysis (as oxygen is needed for the tricarboxylic acid cycle and electron transport chain). In contrast to aerobic respiration wherein 36 ATP is produced per molecule of glucose because of the tricaroboxylic acid cycle and electron transport chain. Aerobic respiration is 18 times more efficient than anaerobic respiration.

The overall efficiency of aerobic respiration is around 40% and since aerobic respiration is 18 times more efficient than anaerobic respiration, then the overall efficiency of anaerobic respiration is around 2.22%.