How important is pack fit?

I think I may have made a mistake recently and completed a trade for a brand new Osprey Atmos 65... Normally, I would be ecstatic, but I totally forgot to check the size of the frame (I assumed the person I traded with had a frame that fit him). As it turns out, the frame is a large, and I am most definitely a medium. Is there any way to make this frame work, or should I just try to sell it and purchase one in my size?

For those interested, I am 5'9 and about 180

First, welcome to the forums.

With regard to the pack, I think you’ll probably have a near-impossible task trying to make it work. (The only thing I can think of that is as important as a properly-fitting pack is properly fitting shoes or boots.)

Are you a medium in Osprey packs, or a medium in another brand? (“Medium” can be different for different brands.) However, before you give up, do two things:
1. Load your typical load of gear (including food and water) into the pack, as you would for a weekend trip, and try it on; play with the various adjustments on the suspension, to see if, by chance, it will work.
2. Since it’s loaded anyhow, take it to the shop where your friend bought it (if you can; if you can’t, take it to REI - they’re good about helping), and let them take a shot at making it fit you correctly.

Then, if neither of those things work (they probably won’t), start looking for a new pack. You might be able to sell the one you have, or at worst use it to help someone else get on the trail.

Good luck.

Welcome!

You may want to read this useful article on backpack fitting on the home page of this site. Note that the important measure is your torso length, described in the article, not your height or weight. The size (small, medium, large, whatever) is liable to be a different torso length for each pack maker, and sometimes even for different models from the same maker.

If your backpack doesn't fit properly, you can be in for a lot of misery, so please do whatever it takes to find a good fit. All of you, from your shoulders to your toes, will thank you!

Good advice from Glenn and OM. Also, check out Osprey's site:

https://www.osprey.com/us/en/fitting-learning/size-fit

In the "old days" when there were not sufficient sizes in packs, I always had a pack that was too big for me. It just makes it more uncomfortable, not impossible. If the hip belt fits, then the length is less of a problem. If the hip belt does NOT fit, then the pack is pretty much useless. A lot of packs have removable, interchangeable hip belts that can be replaced with as smaller one.

Experiment with packing it differently. Keep heavy items near your back and not above your shoulders. Try it for a while before you totally give up. It may not be as bad as you think.

The best way to see if it will work for you is to load it up and put it on. Walk around with it on and try to note what feels good, what doesn't. Then go down to your local outdoor store, assuming you have one, try on different packs with a load in them and try to make comparisons to the one you have. If they have that Osprey model in a medium, all the better, load it up and put it on for a while.
Just because your pack is a large and you feel like you're a medium, doesn't mean it won't work for you. The fit of every pack is unique, the more you try, the better your chances will be of finding the perfect one for you.
Good luck!

Bummer, it appears that the Osprey's do come in sizes rather than offering adjustment options. I have used Deuter for a while now and it is very convenient to be able to adjust the fit when I lend a pack to a friend.