Put all your gear in a bag, see if you can make it somewhat rectangular and measure the width, height, and length. Say you get 15"x 30"x12" . Your total cubic inches = 5400. You need a larger size pack or something in the 90 liter range. Now that's a big expedition pack, but you get the idea. That size can be reduced by strapping things outside the pack, like a pad or your tent. Not all packs will carry the same, nor pack the same. Some are narrow and will not hold a bulky sleeping bag, or have an opening that is too small too fit one in. Some have more capacity in outer pockets than the main compartment. Some have the capacity primarily in one big bag. Some have a sleeping bag compartment, but most will only take smaller, compressible bags, not big synthetics. Decide what you need depending on what you'll bring. If you want to spend more money to downsize, you can, but if you can't, figure up what you have. If you're an Osprey fan, their website has a good explanation how to fit and size a pack. I recently bought an Atmos 50 and love it. I dialed in the fit exactly the way I want it (lots of adjustments!) and a couple hundred miles of winter trails later it hasn't changed. In recent years I've used much lighter packs and paid the price every time I had to add weighty items like lots of water or things out of my wife's pack because she wasn't feeling well. The fact that the pack is heavy itself is well belied by how well it carries. If you buy from REI or another reputable supplier with a good return policy, you can make sure you get what you need. Make sure your gear is clean, or put it in plastic bags and see if what you thought worked, does. There's a company down towards Harrisburg called Backcountry Edge that could be helpful. I had some conversations with them on the phone and they were very cool. They are also avid backpackers and could even help with places to go in Pa. I would call and have a conversation with them when I thought I had a handle on what I wanted. They're an Osprey dealer, too. https://www.backcountryedge.com/manufacturers.html