Anyone familiar with the granite gear 3.5 pack? Capacity is listed at Capacity: 57 liters | 3500 cubic inches. Assuming thisnos smaller than a #4 Duluth pack…but how much smaller when it comes to packing is in gear?

I have a GG "Solo" pack that is 4000 cubic inches, so just a tad bigger (1/7th more space) than the one you are considering. It could still fit a bear vault (large size) cross wise at the bottom or two bear vaults side by side with a bit of room on top. I liked it for a small adult, or for younger teens. Well built like all GG packs. I'd have more if they still made them.

Depends what kind of party you are tripping with, but I always find a use for a pack about that size. I do have multiple larger packs though, so I think you consider the whole set of options. If the price is right, add it to the mix.

The 3.5 numbers (3500 cu. in. or 57 liters) are smaller than those derived from the dimensions listed on Granite Gear's website (21x26x7 = 3822 cu. in. or 62.6 liters). My guess is that the smaller numbers are based on the draw-cord overflow feature not being used to its maximum. It is a little confusing and I don't have a #3.5, unfortunately.

Compare the GG3.5 to the GG#4: 6000 cu. in. or 98 liters. The published dimensions and the volume match in that case.