So I bought a Gregory Advent Backpack
and am now finding out the hardway that it is too small.
I finally got what I believe is an accurate measurement of my torso
length, 21". The backpack is only rated up to 19.5".
What I don't understand is the largest size is only rated up to 21.5".
I'm only 5'10, What the hell do 6'3 people buy. I was under the impression
that a person of my stature should only be around 19".
Anything weird here? I'm not too worried about it because I think it's going to fit my Wife just barely. Thanks for any insight.

I'm 5'10" and my torso is about 19". My medium Advent Pro fits fine.

How exactly are you measuring your torso?

In what way is the pack too small?

Perhaps you're wearing the hip belt too low?

If I'm reading your post correctly, you bought a medium. Given the size of your torso, if measured accurately, why didn't you buy a large?

Hey Trailrunner- You are correct, I did buy a Medium.
It was on sale and the only size left. I was in a hurry and thought
it would fit. Obviously I paid for my mistake.

I believe it's too small because it's riding on my shoulders. I did a
approximately 2 mile hike with little weight and it was already hurting my shoulders. To be fair to the pack however, I did workout my shoulders
in the weightroom the day before.

But again, I did measure my torso using from the designated instructions for various websites (gregory, REI). I measured 3 times, Got 21.5, 20, 20.

Did you have someone else measure your torso length? I tried to do it myself three times and came out with three different measurements ranging from 16" to 17.5". Finally I got a friend to do it. Both she (with measuring tape) and the local REI store (with their pack measurement gizmo) came up with 15". REI has an excellent video on their website how to do the measuring and another one on how to adjust a pack.

And did you have your torso measured by someone else before you ordered the pack?

Your height has little relationship to your torso length. Some people have longer torsos and shorter legs, while with others it's the opposite. That's why the torso measurement is so critical, and is not something you should do yourself.

You could get a pack without a hip belt. Or just not use it. I hardly ever use my hip belt. I used to think I would fall off the trail and perish without a hip belt until I quit using it and now I never notice its there. Then you could use any pack you wanted-I think.

You may be just outside the size range for a medium.

Have you used the load lifter straps? They take weight off your shoulders. Or try shrugging your shoulders while cinching down the hip belt.

If that doesn't work, oh well your wife can enjoy it.

Or......maybe you can still return your medium and get the large on sale here with free shipping.

I think it's a great little pack. I have the older model with mesh pockets.

Yeah, you need a large. I have one of those, and the more I use it the more I like it. It even handles overloading at the start of trips well -- astonishingly well for a pack so light.

I've noticed the same thing. My torso is a bit longer than an average person for my height which s 5' 11". I've been unable to find a pack as well.

It's not necessarily weird to have above or below average measurements. I have short legs but my torso is 19"... I'm 5'5" tall.

I'm on the other end - 6'3'', 19in torso.