An airbed system, connectable to an air mattress chamber of an air mattress, includes: a pressure sensor, configured to obtain pressure measurements corresponding to the air mattress chamber; and a control unit, configured to operate a pump and valves of the airbed system to inflate and deflate the air mattress chamber, and to determine first and second constants corresponding to inflation of the air mattress chamber and third and fourth constants corresponding to deflation of the air mattress chamber.