Tube Length for Mortar tubes

Dumb question, I am new to building my own mortar tubes for artillery shells. When it comes tocthe tube length, I have to add the 1 1/2 for the base correct? So, a 12" tube in reality would be 13 1/2" in total length?

Good Evening. I just saw this question. My 15" tubes are 15" overall. Same with my 12" tubes. They measure the outside length of the tube and don’t count the plug at all. Hope this helps.