Bushwalk Australia

Pack manufacturers usually specify the volume, height, width and depth of a pack. The volume is expected to be significantly less than the product of the height, width and depth since the packs have rounded corners.

Is it safe to assume that a fully loaded pack will be no higher than its specified height, no wider than its specified width, and no deeper than its specified depth? If not, what is the meaning of these specifications??

What got me started on this question is my interest in the Aarn Peak Aspiration pack. The Aarn web site lists (for the long option) the following dimensions:

Height: 65cm

Width: 34cm

Depth: 20cm

The product of these dimensions (6.5 * 3.4 * 2) is 44.2 l. The Aarn web site specifies the volume as 50 l. As far as I can see, this means that one or more of the dimensions must be incorrect - the volume can certainly be less than the product of the height*width*depth, but it is impossible for the volume to be more than that!

Am I missing something here, or is this simply an error on the Aarn web site?

depends, depth and width can actually be variable, a lot of designs the outward faces of the packs are designed to curve, so the packs are like an oval shape looking from above... so the depth varies. plus they may count pockets in the size which is additional to the stated dimensions often...
i know a pack tester who would fill packs with foam chips and take the volume of the chips to work out the pack volume..

wayno wrote:i know a pack tester who would fill packs with foam chips and take the volume of the chips to work out the pack volume..

Humm A simpler way might be to suspend the pack on a luggage weighing device -
put a plastic bag inside and fill it with water ... the weight gained in kg = capacity in litres.
This would miss any outside pockets etc. those too could be tested in a similar way.

You may be missing something, yes.
"Most major backpack manufacturers measure the volume of their backpacks by adding up the total volume of the closed storage on their packs, including the main compartment, pockets, and hip belt pockets that can be closed or zippered shut. However, many smaller manufacturers use a different method and include open pockets like side water bottle pockets or rear mesh pockets in addition to the closed storage. This can make weight-to-volume comparisons a little misleading when comparing packs from different manufacturers"-sectionhiker.

This is the sectionhiker quote for the Osprey Talon 44
"If you’re looking at the pictures in this post, you’ll see that the Talon 44 liter backpack holds a lot more gear than the 40 liter backpacks made by many cottage gear manufacturers. That’s no accident. Osprey adheres to an industry standard for computing backpack volume that only includes closed pockets, and not the open side bottle pockets, hip belt pockets, or rear mesh stuff pockets that are counted by most cottage manufacturers. This is helpful to know about when comparing backpacks. If you were to add those pockets into the Talon 44 volume calculation, it’d probably be equivalent to a 55L – 60L ultralight pack made by a cottage manufacturer" i.e Granite Gear Crown.
Which measurement system does Aarn use? "Cottage" perhaps?
Ring the manufacturer and ask what they include in their litreage is the best bet.
Cheers

The pack height is probably measured with the pack adjusted like the photo on the Aarn website. But loosen the straps that hold the lid down, let the lid ride up, fill the storm throat with gear, and you've probably gained six litres. Put a one-litre water bottle in each of the side pockets, and you are up to the specified figure of 50 litres.

When BackpackingLight did backpack comparison it found that most were smaller than indicated, some by more than 20%.
That is why I typically suggest not to compare pack sizes by the manufacturers figures but by what you can in fact fit in.
(of course you need to go to a shop to be able to do that or spend more money on postage)
As for the Aarn pack, I would think that the two side and the front pocket are taken into consideration.