The range of medical oxygen cylinder sizes goes from M-2 to M-250 and includes M-4, M-6, M-7, M-9, M-22, M-24, M-60 and M-122. The diameter sizes range from 2 1/2 inches to 52 inches, and empty weight ranges from 0.7 pounds to 114 pounds.
Each patient using medical oxygen has unique lifestyle factors that make different sizes ideal. The most frequently used size is the M-6, which weighs 2.2 pounds when empty and is easy to carry in a bag. Patients who are confined to wheelchairs often use a larger cylinder with a wheelchair bag, while those who only rarely leave home and have extremely high weight use the smaller M-4.