I am a 5'9", 63yr old average, moderately athletic female for reference. I LOVE this backpack. I must say I have not used it though. I packed it but didn't make it on a flight to Spain/Portugal. I plan to use this instead of a rollerboard carry-on suitcase. Let me tell you, it holds A LOT! Just as much (maybe more) as my 21" roller carry on suitcase. Fully packed it was 13lbs and felt heavy to hold in hand but VERY VERY light on my back! It is about 25 inches tall (unpacked) so exceeds the 21" requirement (20" international) carry-on size but with all the compression straps it looks smaller. Also it has 2 aluminium back support bars inside that are removable and worse case scenario can be removed and repacked inside diagonally or attached outside to make the bag further compressible!! It packs like a suitcase since the whole front flap opens with 2 zippers down to the grey bottom. It has 2 compression straps inside but they are attached to sides inside so don't compress 'down' but pull sides in. This can also be a top load backpack. It has 2 drawstrings on top. One for normal closure and one to extend this bag up and make it larger. I use the little pouch it makes for my toilet kit for easy access. (I put my 3 qt bag of liquids in the fanny pack for easy TSA access). There are 2 compression straps across the front again on the outside. Handy to put another daypack under if you wish. Then there are 2 compression straps top to bottom that actually are attached about 2/3rds of the way down (making them into 4 straps actually) so you can attach something(sleeping bag/tent) on bottom front area and still compress rest of bag. There are large billow pockets on both sides that run top to beginning of grey bottom. I pack a coat in one for quick access. The sides also have 2 compression straps. *The picture shows a third compression strap over water bottle pockets. It's NOT on this bag. There is a large elastic topped pocket in each side for water bottles etc. They are from front to back so will probably hold any size bottle. I like that they are not webbed and more sturdy canvas. The harness is adjustable to practically any size torso it seems. I'm a 20-21" torso and I set it to Med.It has xsm, sm, med, lg, xlg adjustment area with loops and very secure velcro. The back is comfortably padded and webbed for air flow as is the waist belt. The belt is removable and therefore moves with your hips. I plan to remove the belt if I have to check-in the bag at the airport. I also would put the (bright orange) rain cover on it to protect it a little or contain straps. The rain cover is NOT attached by the way. The top is removable as a fanny pack. Belt is included. It is a little weird though. The underside only folds/snaps together leaving it open (body side) which is ok to stuff a jacket or towel etc but the only sealed compartments are the zippered top outside and a slightly smaller inside zippered area. It's just suppose to be a fanny pack not daypack. I was hoping use it for my Canon 70D camera but I will have to use my camera daypack. I will not be using this as a fanny pack. I'm a little worried that the outside zipper on this top/fanny pack will not hold up. There is a waterproof zipper covering that is invisible. It's like just zipping rubberized material together so I wonder if it will wear out eventually. Zipper is well built though. There are also 4 slits sewn on to attach straps through. The shoulder harnesses are comfy except the webbing will rub if you are bare shouldered like with a tank top. I plan to cut the foot off some soft knee high socks and slip them on the straps. There are straps for trekking poles also. Lots of straps to adjust load weight also. I will use this on an upcoming flight to Scotland in October and update this if needed.