Forced vital capacity: the maximum amount of air you can forcibly exhale from your lungs after fully inhaling. it is about 80 percent of total capacity, or 4. 8 liters, because some air remains in your lungs after you exhale. forced vital capacity can decrease by about 0. 2 liters per decade, even for healthy people who have never smoked. The healthy lung function percentage higher your percentage, the larger your lung capacity and the healthier your lungs. your doctor will diagnose copd if your fev1/fvc ratio falls below 70 percent of the predicted value. The average maximum capacity of a healthy lung is determined by a person's height and varies. the average is approximately 6,100 milliliters (mililiter), 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. Pulmonaryfunction tests (pfts) are used to assess various aspects of your lung function. these noninvasive tests—...