This canvas and PU leather (whatever that means!) bag has a lot of good features.  It has several inner pockets in which to store smaller/more important items.  I measure it to be 7" by 18" by 12" with my tape measure.  It can be cinched down with straps or expanded to the dimensions I just listed.  It has a large outer pocket the size of the entire 18" by 12" which opens to reveal shoulder straps so it can be worn as a backpack and there's room in that pocket to store items if the shoulder straps aren't being used.  It has several zippers to access different larger pocket areas, which make it easy to access things, while dividing sections in the bag to allow you to compartmentalize your belongings.  Really a nice bag...maybe not as large a storage bag as some of the carry-on bags I've seen on planes, but would hold a decent amount of items. Also it's probably heavier than a nylon backpack would be and may not be very waterproof.