To calculate the approximate volume of a scuba cylinder you will need to obtain the following information about the cylinder: diameter in inches, overall length (without valve) in inches, working pressure in pounds per square inch (PSI), and the cylinders material (aluminum or steel).  With this information you can use the following formulas.

 

for steel cylinders:

 

   

It will come out in cubic feet

Length is the total length from the base to the top of the o-ring gland in inches

dia is the outside diameter in inches

working pressure is in PSI

This formula gives an approximate volume, usually within 1 cubic foot, for standard steel scuba cylinders.  However for Pressed Steel Tanks (PST) cylinders made under DOT E9791 it is off by almost exactly 5 cubic feet.  Rather then use the formula for E9791 cylinders, the physical measurements should be compared to PST's promotional publications which provides specific measurements and volumes.  This formula has not been tested with other cylinders less common in the United States (international Faber, Ashi, or Heiser cylinders) and may be less accurate for those.  In those cases the manufacture should be contacted if the exact volume is needed.

for aluminum cylinders:

that will come out in cubic feet also.

This formula gives an approximate volume, usually within 1.5 cubic foot, for standard aluminum scuba cylinders. Due to the different wall thickness of the smaller cylinders it should not be used for 15 cubic foot and smaller cylinders.  Additionally, the exact volume of all Luxfer and newer Catalina cylinders may be found by comparing the serial number to publications from each manufacture.

Written By Corey Monahan
PSI Course Director
March 24, 2004