Tests say claimed backpack volumes not even close

Forum Posting

A Membership is required to post in the forums. Login or become a member to post in the member forums!

Home Forums Gear Forums Gear (General) Tests say claimed backpack volumes not even close

Viewing 13 posts - 1 through 13 (of 13 total)
  • Author
  • #3710813
    Rex Sanders
    BPL Member


    Interesting story from Mike Unger and Naomi Hudetz at Treeline Review:

    How Accurate are Stated Volumes of Backpacking Backpacks?

    In short, not very.

    They used pinto beans and measuring cups to fill six backpacks from five well known lightweight pack makers.

    The measured volumes ranged from 10% less to 39% more than the claimed volumes. All were at least 10% off.

    A theoretical 40 liter backpack main body might actually be 36 liters, 44 liters, or even 56 liters! Could explain a lot of mysteries.

    Read the story for all the deets.

    — Rex

    Andrew Marshall
    BPL Member


    Locale: Tahoe basin by way of the southern Appalachians

    I know a lot of brands are starting to stipulate that their total volume includes exterior pockets, but that seems like it might be even MORE subjective and hard to measure.

    BPL Member


    I’ve found McHale’s method of using pack circumferences to compare relative volumes to be the most useful. That method does break down though when comparing against packs with highly curved back panels (Osprey Exos, Seek Outside Flight).

    Todd T
    BPL Member


    Locale: Pacific Northwest

    The article doesn’t say, but I hope they were careful to get the correct claimed volumes.  Most mfrs seem to quote volume only for one torso size, usually Medium.  Until I sold the smaller one, I used to own both a Large (21″ to 24″) and an Extra Large (24″ +) ULA Catalyst.  The latter has noticeably greater main-body volume.

    Dustin V
    BPL Member


    Sounds like they found out how much chili you can carry. But seriously, folks… it is frustrating to look at two packs that are supposed to have the same volume and see that one is bigger.

    I do appreciate that some manufacturers are listing the size of the external pockets, especially if they’re large pockets. It gives an idea what I can carry in the pockets and what I need to fit into the main.

    Dan @ Durston Gear
    BPL Member


    Locale: Canadian Rockies

    I don’t think this articles explanation makes sense. They write:

    “We suspect that volumes labeled on backpacks are influenced by marketing and giving consumers what they think they want in a pack…..Brands advertise their pack volume based on what consumers think they want in a pack.”

    That sounds scandalous but doesn’t make sense because gear companies can simply design a pack to be the desired size -they don’t have to make a pack in the wrong size and then lie about the size to woo customers.

    And they write:
    “We found that we could fit the same gear in a so-called 35 L pack that we could fit in a 55-L pack.”

    Which again sounds scandalous but it’s really not when you realize it’s simply because they are comparing dissimilar specs. Both of the “large” packs they review (Mariposa 60, Air Blast 55) openly disclose that their headline number includes the external pockets and the internal capacity is less at 36-42L.  So the fact that they are similar to other packs that claim 35-40L for just the main compartment shouldn’t be surprising. The real message here is not that the specs are off, but rather than customers should read them.

    Comparing their observations to the actual claimed specs (e.g. main compartment vs main compartment) these packs really aren’t that far off. The average main compartment spec is 37L and they observe an average of 36.5L – but of course that doesn’t make for much of a headline. A few are off by a decent amount (up to 8L) but nothing like 20L as you’d think from their text (e.g. 55L is same as 35L).


    BPL Member


    Looks like Dan has the right of it.

    BPL Member


    Dan makes a lot of sense.

    Of course this is probably the only instance of specs creating false expectations.  Hahahahahahahaha

    Michael B
    BPL Member


    We used pinto beans to fill the main compartment of packs. For roll-top packs, we filled until we could roll the pack 3 times. The same person measured all the packs on the same day.

    while this is nice to make comparisons, this methodology is likely not what the manufacturers use for their measurement. It is pretty easy for a buyer to check dimensions, and if clarification is needed, send an email, all these companies are pretty good about their customer communications.

    Roger Caffin
    BPL Member


    Locale: Wollemi & Kosciusko NPs, Europe

    However … When doing a survey of internal frame packs I found that while most mfrs were fairly honest (ie my measurements matched their claims), a few mfrs were blatantly dishonest.

    One I remember stuffed the main bag really full and recorded that volume, then they emptied the main bag and stuffed the back pocket really full and recorded that volume, then they repeated that for the pocket in the lid. Then they added those numbers up and claimed the result.

    But you cannot do that in real life. If the main bag is full, then the back pocket is almost unusable, and so on. I challenged them, and they admitted that was how they did it and if I didn’t like it I could go jump. Known brand, too.


    James Marco
    BPL Member


    Locale: Finger Lakes

    There is a huge difference in how people think of things and how some packs packs can seem larger than spec. For example a 10x10x10 pack will hold 1000ci. But a circumference of a 40″ barreled out pack, to form a tube approximately 9″ long, is actually much larger at about 1146ci…roughly 15% larger. So, besides the measuring discrepancies between manufacturers that Roger points out, packing between users also effects the size.

    Most light packs are usually based on a rectangle about 11″x20″x6″ or roughly 1320ci. Then they usually have one front pouch roughly a semi-tubular shape about 11″x12″x4″ or roughly 450ci. Then they usually have two pouches, again semi-tubes, roughly 8″x6″x6″ or roughly 225ci. for a total of 1995ci or ~33L. As a check this is within the realm of reason-ability even of the exact dimensions vary.

    Long ago I just quit worrying about the exact numbers the manufacturers released. They never jived with what I was expecting unless I just calculated out approximate volumes from their specs. Tow packs from different manufacturers can vary wildly, often by as much as 25% WITH NEARLY THE SAME SPECS. It seems like the makers don’t really want us to have a grasp of how big a pack is. Or, a scary thought, they don’t really know.

    Roger Caffin
    BPL Member


    Locale: Wollemi & Kosciusko NPs, Europe

    Or, a scary thought, they don’t really know.
    But they do know what their competition is claiming.

    I once asked a local mfr of sleeping bags how he tested his bags, given that he had ratings like -10 C, -20 C and so on. His honest reply (because I knew him) was that he didn’t ‘test’, he just compared his bags with the competition.

    Maybe Standards do matter?


    Michael B
    BPL Member


    If one is looking to jump brands, then standard metrics are useful, but if just moving within a brand, probably not as useful. I can always appreciate objective metrics but they aren’t always needed, especially if I am able to try something out. Not many a huge outcry for pant and shirt suppliers to provide exact measurements, with weight usually being the exception (for us weight weenies)

Viewing 13 posts - 1 through 13 (of 13 total)
  • You must be logged in to reply to this topic.
Forum Posting

A Membership is required to post in the forums. Login or become a member to post in the member forums!