Your doctor may want to test your total lung capacity for several reasons: 1. to penaksiran lung diseases and differentiate restrictive (e. g. pulmonary fibrosis) from obstructive (e. g. asthma or chronic obstructive pulmonary disease, copd) types. dua. to determine the severity of copd or asthma 3. to evaluate if you're a good candidate for lung cancer surgery2 the average maximum capacity of a healthy lung is determined by a person's height and varies. the average is approximately 6,100 milliliters (ml), which is equal to six liters, or approximately three large soda bottles' worth of air. this benchmark can help doctors determine if lung function is compromised. for example, in patients with copd, the amount of air left in the lungs during the breathing process is usually more than normal. patients with copd are often unable to exhale fully, resulting in hyperinflation of the lungs. 2. The centers for disease control and prevention publishes standard values for lung ...