first backpacking trip - liters vs physical size

I'm going to South America for a month and the 38L pack I've tried was a little overstuffed, with little room for things like souvenirs. I'm confused though because I found a 60L pack that was actually smaller in terms of inches. Anyone know how that's possible?

Also the airline told me 45" was the max overall size for a carry-on. So I'm also looking for suggestions for packs that are roughly 50-60L and smaller than 45" -- thanks!

ok, first this forum is dedicated to the American definition of backpacking (which is wondering around the woods with a shelter) and not the European definition of backpacking (budget travel). You seem to be more interested in the later.

Either way, I think there are people here who can answer your question. There are no standards on how a company rates the size of there backpacks. As a result you can get much variation from brand to brand. As to why a longer backpack would hold less, that can be as a result of the other two dimension (width and depth). Backpacks are really tricky things to buy and the most important thing is how they fit on your body. It is really best to go try them out in person. See how much room they have and how comfortable they are on you when loaded up. If you can't try them out at a local shop then focus on companies with a hassle free return policy. Order a couple you think will work and return the ones that don't.

So what do Europeans call hiking in the wilderness with your necessities on your back? (since backpacking is budget travel)

They call it trekking, I believe.

Thanks guys. But even when flying to a place in the US before an outdoor, have you ever encountered an issue with using your pack as a carry-on?

"So what do Europeans call hiking "
Backpaking is also the Aussie and Kiwi term for hostel to hostel/working holiday type travel.
We call hiking "bushwalking" and the Kiwi use the term "tramping" however hiking is universally understood even by the "hill walking" Poms (that is the English)

Most hikers have a pack larger than the cabin allowance so we check it in as luggage, usually wrapped up in a bag to avoid the straps getting ripped out.
Most luggage manufacturers have cabin specific bags (that is made to fit those measurements) including some that have backpack type straps.
http://www.ospreypacks.com/en/product/backpacking/farpoint_40

With my McHale, I pull out my upper bayonet stays and then it fits as a carry on with some of my more expensive/fragile gear inside, such as my sleeping bag.

Colin Fletcher (who claims both European and American pedigrees) called it "mucking about."

Lonely Planet's Thorn Tree travel forum, which after being shut down for a couple of weeks is now coming back to the net, might have better answers from a travel point of view.

Edit, later:Then, again, maybe not, because only a small number of sections on the LP Thorn Tree are up and the old posts are not yet there. There used to be a lot about backpacks used for travel. Do remember that airline baggage handlers are very hard on baggage, so a lightweight backpack, such as most of us here use for wilderness trekking, may not be the best solution for travel.

The backpackers club in the UK has this to say:
No formal definition of 'Backpacking' exists, but perhaps a good description would be the art of being self contained, carrying everything you need to survive in the outdoors such as a tent, sleeping bag and food etc. whilst walking/cycling from one location to another on a multi-day journey through a natural landscape. A good example would be backpacking along a Long Distance footpath. This club is not to be confused with 'backpacker' who may travel by train/plane staying in hostels etc. The Backpackers Club is for those who propel themselves across the countryside whether by walking cycling, canoe or even cross country skiing!

SO backpacking has two meanings, that which we on this forum would generally use, and cheap (frequently urban) travel

Lots of words have two meanings.
Often non US English speakers are aware of both because we are bombarded with American movies and TV shows, however the converse is rarely true.
But just to avoid confusion , don't tell an Aussie that you sit on your fanny and we will not tell you we wear thongs (beach sandals, flip flop, jandal...)

One of the great books of the 70's was "Vagabonding in Europe and North Africa" by Ed Buryn. Obviously outdated today, but it was a great read for those wishing to travel back in those days. When I went to NZ, "Tramping in New Zealand" a Lonely Planet book, was the book to have if you were hiking.

"But just to avoid confusion , don't tell an Aussie that you sit on your fanny and we will not tell you we wear thongs (beach sandals, flip flop, jandal...)"
HAHAHA! Reminds me of when I was standing in Cathedral Square in Christchurch and told my newly acquired Kiwi girlfriend that my wallet was in my "fanny pack." She was like "What?" and burst out laughing when I explained to her what I meant. Kiwis wear a "bum bag," definitely not a fanny pack. Go look it up.

When I was a kid, we called them thongs. But later, as I grew up, I learned what the word also meant, and switched to calling them flip-flops.