Upvote:8
It seems like this is a number the manufacturers give the bag that is close to the largest single dimension of the bag. Looking at some bags on Amazon I see
So if you really care about 20 vs 21 vs 22 inches, knowing it's a 20" bag isn't going to help much. And even if it was right, the next dimension might be 13, 15 or 17!
Your best bet is to search on some other sites for the same bag and hope one of them tells you the actual dimensions. Also, if you can, find out if these are inner dimensions (what you can put in the bag) or outer (where the bag will fit.)