This is going to be fairly basic advice. First and foremost the pack needs to fit you. An earlier post on this thread recommended getting all of your gear first and then looking for a pack that can fit it all. That is good advice.

To find out what size pack you will need you can use the box method. Assemble all of your gear that you plan on putting inside of your pack. Get a large enough cardboard box to hold it all and put your gear inside as neatly as possible. Get the measurements of the box in inches. Length x Width x the Height of your gear at its highest point in the box. Using this formula you'll arrive at an approximation of how big of a pack in cubic inch volume you will need to fit your gear.

Allow a fudge factor of about 10% to 20% more in this calculation added to your final cubic inch result for those things that we all just can't seem to do without and throw into our pack at the last minute. wink

Keep in mind that things like water bottles and your shelter might be carried on the outside so you need to take a good look at the outside pockets and their capacity also.

I carry my shelter in a dedicated side pocket, a quart Gatorade water bottle on the other side, FAK in a smaller outside pocket near the top of the pack and my water treatment etc. in another smaller pocket also near the top of my pack on the other side.

My rain gear and other sundry items fall into the large main front mesh pocket. I also carry two 28 oz water bottles, one on each side, attached to my shoulder straps.

All of this was meant to help you determine a volume / size for your pack. Remember that fit, comfort and pack weight are also prime considerations.

Get the lightest pack that fits you the best that can comfortably carry all of your gear.

Enjoy your trip!

Newton cool
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One day on the trail is 100 times better than one year on the couch!