Help Gas tank question

[Alos]

When buying gas like N or H, or CO... Does the tank need to be 4 feet for the length of time or the amount of gas in the tank? Like if I had 6 smaller tanks, would that also work? Or do I need the larger tank because it last the right length of time?

 

[locked*n*loaded]

Automatic Changeover Regulators

 

[GasMonkey]

A small 20ft³ cylinder has gas for 37 minutes at 15 LPM.