I bought this bag for school and traveling with my laptop, knowing that this would not be my edc bag. I love Osprey bags, I think their shoulder straps/suspension and back panel on this pack are spot on with what I expected from them (I have the Kyte 46 and Daylite that I love). Getting through TSA with my laptop was super quick. I ended up zipping through in front of 2 people that were fighting to get their laptops out of their bags as I just unzipped mine - so that was pretty awesome. As for fitting under the seat - I did not have this bag packed full so I was able to stuff it under the seat. If it was stuffed full it would have been another 2-3 inches or so deeper and would not have fit under the seat (Spirit under-seat limits are: 18" x 14" x 8") The bag is at least 19" x 12" x 10", although I did not measure to confirm. I used 2 medium ebags packing cubes fully packed and had my 15.6" HP laptop in the back, there was room for a lot more in the bag, but I wanted it to fit under the seat (see photo attached). Note: I was able to pack pjs, and 2 days of clothes, a bathing suit and undergarments in the 2 cubes. My complaints with the Osprey bag is a complaint I have with a lot of bags/packs -- the side compression straps go around a water bottle. When you take the water bottle out, the bag is not compressed, this is just annoying as it makes the bottle harder to get out if you have the straps pulled tight. Other than that, the organization and compartments in this bag are great and provide a space for everything I need for class.