I bought this duffel bag because I have a lot of gear for snowmobiling and was tired of using trash bags that rip all the time.  I really wasn't expecting the x-large one to be THIS big though.  I can get my snowmobile suit, BIG winter boots (size 15's), two gallons of oil plus all my clothes for a 4 day trip in here.  OMG.  I may not be able to lift it when I get it packed though.  :)  The sizes are as follows:  X-Large: 16" x 18" x 36";  Large: 15" x 15" x 30"; Medium: 12" x 12" x 24".  I could definitely have gotten away with a smaller one but oh well, less trips I have to make into the cabin now.  Ha, ha.  This size bag comes with a travel pouch for your toiletries or other things that you'd want to keep separate or for storing this bag after your trip completes.