The object of the invention is to simplify the method for controlling the air volume in a closed air supply installation. To this end, the pressure of the pneumatic springs (3, 4) is first determined when air is let out of the pneumatic springs (3, 4) into a defined control chamber, the average volume flow of a defined controlling process between the air chamber (5) and the pneumatic springs (3, 4) is determined, and the pressure in the air chamber (5) is calculated from a functional dependency in relation to the determined pressure in the pneumatic springs (3, 4), the determined average volume flow and the measured external temperature. The pressurised air volume of the air supply installation is then calculated from the calculated or determined pressures, the known or determined volumes of the air chamber (5) and the pneumatic springs (3, 4), and compared with an optimum pressurised air volume.