Lungs come in different sizes, but the amount of air that a person should inhale is quite constant. There is a standardization table for that. The measurement of the volume inhaled and exhaled by a person is measured with a spirometer.
It is usually used for preliminary pulmonary tests to test a person’s lungs, and also finding causes of shortness of breath and so on.
Modern day spirometer can be connected to the USB of a pc and the results can b seen on the screen.