i don't see (maybe i missed it?) that anyone said you have to be measured for a pack, just like for shoes. Everyone's backbone is their own, no matter their total height. Even the flair of hips, width of shoulders, volume of chest, and etc. Are a four dimensional puzzle. So, for a hike of any length, it's helpful to have the right pack, and that doesn't mean the right brand, model, volume, or color. It means it fits your unique body. Only way to tell is to start with a knowledgeable staff who can measure you and then suggest a variety of packs, then allow you to try them on fully loaded with weights (a good store has weighted sacks) and let you walk around for a while with each pack.
But i can tell you from experience, that even that is not perfect. Only a long-distance hike can tell you for sure. My daughter worked in an outfitter store before her thru-hike and she still switched out her pack after a few weeks on the trail.
I can also tell you that it's not just the pack, but other issues, such as what you load in it and where, and what you wear under the pack. I got a new pack this summer and it promptly rubbed a raw spot on my backside due to the underwear i was wearing on a trip.
It's all a balancing act and not one we can readily and assuredly answer for you online based on a tidbit of data. So, experiment. Hopefully buy from a store that allows returns. And don't expect perfection, just fun.
Rain
man
p.s. There's a saying that if you buy a big pack, you will fill it up, so buy a small pack.
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