The correct way to measure lung capacity is by using a spirometer or by doing a pulmonary function test. To measure lung capacity, a spirometer can be used. After the first measurement is given by the spirometer, the tester should take a deep breath and then exhale slowly and forcefully into the spirometer until he/she is unable to exhale. In addition, after the spirometer gives the second measurement command, inhale deeply again and then blow hard into the spirometer. At this point, the spirometer will take the maximum test value as the final value of lung capacity. It is recommended that the spirometry test be performed without interruption. When blowing, the mouthpiece should be close to the face, so that the blowing gas cannot escape through the gap between the mouth and the face. In addition, the blowing should not be too fast, the speed is easy to slow down, and the gas needs to be exhaled evenly.