Tests say claimed backpack volumes not even close

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.

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).

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.

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.

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).

Looks like Dan has the right of it.

Dan makes a lot of sense.

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

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.

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.

Cheers

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.

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?

Cheers

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)

One thing that really bugs me about claimed pack volume is the Zpacks Arc line of packs-which I love. For example, their Arc Blast advertised at 55L, which is total including 2 side pockets and the large mesh back pocket. Problem is, when you max out the main compartment(42L) that pushes into the mesh pockets claimed 8L of storage. When I fully pack the main body,  I am lucky to get a couple of liters worth into that ‘8L’ pocket due to the mesh being so tight.  This feels wrong.

I have measured a lot of pack volumes to the Standard some years ago:
https://backpackinglight.com/lw_internal_frame_packs_part_1a/
https://backpackinglight.com/lw_internal_frame_packs_part_1b/
https://backpackinglight.com/lw_internal_frame_packs_part_1c/
https://backpackinglight.com/lw_internal_frame_packs_part_2/
Some brands do measure their pack volumes properly.

Others measure each individual compartment and then add all those volumes up. As Brad mentions, sometimes you can NOT get anything into compartment B when compartment A is full. Basically, those claims are a fraud. What I wrote in my review in 2010 follows:

Quote

Estimating Pack Volumes

Everyone wants to know what the pack volume is, and manufacturers all oblige by quoting figures. But exactly what value to place on the quoted figures is not that obvious. There are several reasons for this.

I do remember one manufacturer quietly explaining to me that he got his pack volumes by comparing his packs with the oppositions’ packs. He didn’t actually bother measuring his packs. We are not suggesting that this was done by any of the vendors in this survey, but it certainly does reflect the problems.

Trying to <i>calculate</i> the pack volume is hopeless: none of the shapes are either square or round. About the only reliable way to calculate the volume of the main bag is to fill it up with something like sawdust or foam ‘packing peanuts’, and then to measure the amount used in a nice rectangular box which can be measured. But even then there are questions: do you fill the main bag to the top of the main fabric body, or to the top of the throat? Do you insist on closing the throat right up, or just a little bit? There are no definitions in this game.

But it gets a lot worse once you have ‘measured’ the main bag. Many USA packs have mesh side pockets, and how you ‘measure’ their capacity defies imagination. The mesh may or may not expand, and may or may not be sewn up the side. But even more important is the shape of the main bag behind the side pocket. If the main bag is stuffed full you may find that the curve of the main bag almost fills the mesh side pocket right up. Alternately, if you insist on putting something into the side pocket you may find the object intrudes into the main bag volume.

Some packs have a fabric pocket on the back: exactly the same problems apply here. Sure, you can stuff your whole tent into this back pocket (why you would do this is open to question), but doing so takes a significant lump out of the main bag volume. Some packs have a large pocket on the lid, and the same problem arises here too. Some packs have bungee cord looped across the back or the top: should you count these in assessing the volume?

For this review we will quote the volume of the main bag with the top of the throat pulled shut. This figure we can measure. We will comment on the possible capacity of the side pockets and other pockets, but these compartments will not be given equal weight.

Endquote

Cheers

Some stated calculations of outside pocket capacity border on the absurd. ULA claims the side pockets on the Circuit hold 6.6 liters EACH. Those pockets are so small and poorly designed  you would be hard pressed to keep a small bottle of water in the pocket without it falling out, much less what amounts to claiming each pocket can hold almost 2 one gallon milk jugs.

ULA also states the front outside pocket holds the same capacity as each side pocket even though it is st least twice the size of the side pockets.

Those pockets are so small and poorly designed  you would be hard pressed to keep a small bottle of water in the pocket without it falling out

There is so much subjectivity to our experiences. I love the pockets on the Circuit (almost as much as the Ohm). I find them to be extremely secure while also being reachable with a pack on. They aren’t as secure as the pockets on an MLD Burn/Prophet but I can’t get a bottle in/out while wearing those packs.

6.6 liters in each side pocket seems absurd unless they did something radically different than before. I used to put two 1l Smartwater bottles in each side pocket. There was still some room but not enough for a third 1l bottle, much less several more.

Those pockets {on the Circuit} are so small and poorly designed you would be hard pressed to keep a small bottle of water in the pocket without it falling out, …

I’m wondering if you and I are talking about the same pack.  One can like or dislike those pockets, but I can’t imagine how you’d call them small.  I can fit two one-liter Nalgenes in each side if I loosen the top bungees, but with the bungees appropriately snugged down, a single Nalgene (or Gatorade) is extremely secure.

6.6 liters seems an awful stretch, though.

Those ULA Circuit pockets look big. Much bigger than the Arc pockets. When main body is full on the Arc, I can get 1 1L smart bottle and my folded up tyvek doormat and footprint which is small or 1 1.5L smart bottle but it’s maxing out the fabric to the point of tearing.

Why not just put two trash bags filled with water to measure pack volume? Everyone has trash bags and water. Instead of peanuts or ping pong balls etc. Measure from bottom up to shoulder straps first, then fill from bottom to roll top rolled 2 or 3 times and buckled.

Side pockets – use either smartwater or nalgene water bottles as reference. Say how many bottles fit. Everyone has Smartwater or Nalgene bottles.

Yes! I like measuring side pockets by a known bottle like a Smartwater. Several brands seem to do that.

Why not just put two trash bags filled with water to measure pack volume? Everyone has trash bags and water. Instead of peanuts or ping pong balls etc. Measure from bottom up to shoulder straps first, then fill from bottom to roll top rolled 2 or 3 times and buckled.

Side pockets – use either smartwater or nalgene water bottles as reference. Say how many bottles fit. Everyone has Smartwater or Nalgene bottles.

The water idea is good. Add a gallon(3.78L) at a time using an old milk jug poured into a trash bag.

Is there no push for some ISO standards for measuring a packs volume? All external pockets/mesh or otherwise need to be measured with a full main body.

Yes, there IS an ASTM Standard for measuring pack volumes. It is
ASTM F2153-07(2018)
However, it is a commercial deal: you have to pay for it.
As far as I know, there is no ISO standard for this so far.

All this and more is fully discussed in our published articles
https://backpackinglight.com/lw_internal_frame_packs_part_1a/
https://backpackinglight.com/lw_internal_frame_packs_part_1b/
https://backpackinglight.com/lw_internal_frame_packs_part_1c/
https://backpackinglight.com/lw_internal_frame_packs_part_2/
The measurements in these articles conform to the ASTM Standard.

Cheers

Thanks Roger.

I love my ULA pack, but claiming the side pockets can hold 6L each is ABSURD.