The nominal volume of the cylinder refers to the classification series of cylinder volume specified by the cylinder regulations and standards. The nominal volume, like the nominal working pressure, is a nominal value rather than an accurate actual value. For safety purposes, the actual volume of the cylinder must be greater than the nominal volume with a tolerance of +5%. It can be seen that although nominal volume is the nominal value of an appellation, it is strictly restricted and cannot be addressed casually. For example, the nominal volume of seamless cylinder is 40L, its actual volume should be between 40L and 42L.

In order to facilitate management, China divides the nominal volume of gas cylinders into large, medium and small categories: small volume below 12Lites (including 12L), medium volume above 12L to 100L (including 100L), and large volume above 100L.

The volume of seamless steel cylinders is the most common with 40L cylinders, but there are also as small as 0.4L to 80L.

The volume of steel welded gas cylinders, as dissolved acetylene cylinders, is most common in 40L cylinders, while liquid ammonia and liquid chlorine cylinders are most common in 800L and 400L. Because according to the charging coefficient of liquid chlorine of 1.25 kg/L, their medium mass is exactly 1 T and 0.5 T.

The volume of LPG cylinders is the largest with 35.5L. Because calculated with the filling coefficient of 0.42kg /L, this kind of gas cylinder just fills 15kg LPG, which is the consumption of an average family in a month.