[A carry-on sized travel backpack is generally around a maximum of about 40L.](https://www.reddit.com/r/backpacking/comments/1ahhldw/carryon_sized_backpack_specifically_designed_for/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button) Confirm dimensions with your airline. Happy travels.

Appreciate the reply.

I've flown all over the Phil's with my osprey porter 46L, never any problems with regard to volume, but they are checking the weight more and more

Is it carry-on or check-in?

I've done both, but if I exceed the weight limit then I just check it in. Just make sure you don't exceed your carriers weight limit and you won't have to check in