Actual Pack sizes

[JP100]

Hi Guys
The other day I got looking at some McHale packs(pretty spendy custom built job).
On his website there was an interesting page about measuring packs and their real volume vs advertised volume(Pack Volumes - Go Figure!).

For a cylinder pack this volume calculation is quite simple and makes sense, for other pack styles it would be more complex to work out.
You need the circumference of the pack and then from this work out the radius.

C divided by Pi(3.14)= d (diameter)
Then dived d by 2 to get the radius

The area of the circle is simple Pi x r2 (3.14 x radius x radius )

Then you take the area x height of the pack to get the volume.

V= Pi r2 h

I ran this on a few packs I had laying here and its safe to say most are over calculated. I stuffed the bags fill with sleeping bags and did up the draw cord so it was a pretty good measure of all usable space I think. I rounded most measurements down as its unlikely you would ever get all the actual space in a bag filled out and I did have these bags off the frames, so this is probably more than you get in them attached to the frame.

This is what I have got:

Kifaru Muskeg 7000- 5,611 in3 or 91 Liters

Kifaru Argali - 4,161 in3 or 68 Liters

Kuiu 6000 - 4,735 in3 or 77 Liters

Kuiu Icon 5200 Main bag - 3,714 in3 or 60 Liters

The new Muskeg was very noticeable size wise, with a very big circumference of around 48"


I think of the packs I have seen/used the Exo packs seem to be the most realistic with their sizing. I know an Exo 5500 seems alot bigger than an Argali (7000in3 quoted)



Would be good if a few people could add in some other brands/packs to compare???

 

[Lockster]

I have been trying to compare a few pack bags recently too, but more so to see which of a manufacturer’s pack bags would be suitable for me, and I’ve noticed that the circumference and depth is noticeably absent.

Now I honestly think that this particular manufacturer is well known for under calling their volume specs, but it got me thinking that all manufacturers should include that basic information so people can compare fairly

 

[Fedster]

This might interest:

Evaluating backpack capacity in the real world – Bedrock & Paradox

Also, I find measuring backpack volume as if the backpacks were *cylinders* is not that useful. If a pack does actually turn in a cylinder that's called barrelling out, which is a bad thing. Looking at bags as parallelepipeds and doing more complex calcs to find the volume seems to be a more reasonable approach to measure what you will actually get in terms of useable volume.

 

[Lockster]

Wow, yeah, great article, I also enjoy Dave’s articles, but I hadn’t read that one.

I personally would like all manufacturers to show photos of all sides of the pack with all dimensional measurements listed so you can get a real-world understanding if you’re buying it online.

Let’s face it, if you’re replacing a current pack, having the measurements to compare would give a lot of confidence to pick the pack that will work for you. It would also help to catch out sellers that are being a bit ambitious with their stated volumes.

 

[SteveB]

JP, good find. I have an Argali, and it just didn’t seem like 7000ci to me. Using some calculations similar to yours, I got about 5400 fully extended and 4200 filled to top of frame. However, I’ve found the volume of the Reckoning to be very close to spec.

 

[Fedster]

If a bag has external pockets, when you stuff the main bag full it tends to bulge reducing the external pockets -- that is a consideration too in terms of volume, which I doubt it is easy to calculate, but it is there.

 

[Alpinehunter]

I've also thought about pack volume calculations. I've considered filling the main compartment and all of the pockets with something non-compressible like sunflower seeds. Then, you could pour all of the seeds that it took to fill the pack into known volume containers and determine the total volume. You could also weigh the seeds to calculate the volume if you first determined the volume of a given weight of seeds. Never been motivated enough to go through the effort but maybe someday. I currently use trial and error to figure most things out

 

[btg108]

Like this:
https://www.astm.org/Standards/F2153.htm


Sent from my iPhone using Tapatalk

 

[JD619er]

From what I understand Kifaru uses beans to fill their bags to measure volume. I had an argali and if I could post pictures it would look humongous when I had if fill with a full camp and elk meat and antlers. I now have a tahr and it’s listed at 3400 cubic inches I believe. I also had a mystery ranch selway listed at 3600 hundred cubic inches. If I took two picture side by side the tahr is way bigger than the selway with the snow collar extended. Idk if this contributes a whole lot but I just thought I’d throw something out there

 

[Alpinehunter]

Thanks btg! It's not surprising that there is an ASTM method. Makes sense but, as I mentioned, actually doing it would be a pain so I'll go with trial and error. I'll get a bigger pack if my stuff won't fit in my current one

 

[amp713]

I always thought it would be useful for manufacturers to post a pic of it stuffed with sleeping bags and then doing a measurement like that.

But I'm sure not gonna take the time. I'll trial and error it to death

 

[Kevin_t]

We (Seek Outside) try to be consistent and to match or exceed customer expectations. We use a combination of circumference, ping pong balls and trying to make the numbers be accurate to where the product fits.

How does this work in the real world ? Take the Divide for instance (our biggest seller by far), the Divide is more of a UL styled pack (even though it can carry big loads just as well if adjusted for it). In the UL world, most companies disagree with the ASTM spec, and count exterior non zippered pockets. The exterior pockets on the Divide add 800 -1200 in the mesh and bottle pockets, while the main pack bag tested just below 4K via ping pong balls (which seem to count a little low due to large size). In the UL world, many may call the pack somewhere over 5K and in true ASTM spec it would be probably a shade under 4K. Using circumference, if I recall, the Divide was more like 4400 plus exterior pockets. In the end we call it 4500, which we feel is pretty accurate for that customer group.

Now take the Brooks. The side pockets, via ping pong balls were 1185 ish if I recall (each). The main bag, was right around 6K via ping pong balls if I recall. According to the spec, we should be able to count all of it because they are zippered pockets however, when used together a bit of space is lost AND because, when you need a big pack .. you don't want to buy a big one and find out it was overstated so we conservatively put the 7400 number on it although we may have been able to squeeze an 8000 number if we tried.

Hope this gives you guys an idea how a manufacturer sees it. For us, it is more about being accurate to customer perception.

 

[Lockster]

Thanks for your feedback Kevin, if only all manufacturers were as ethical and realistic in acknowledging that volume of side pockets is inevitably lost when the main bag is full, I’d definitely prefer to find out that the manufacturer has been conservative in their estimates, like yourself, than to find that the manufacturer had overstated it just to pull in more unsuspecting customers.

Thanks for your integrity.

 

[pods8 (Rugged Stitching)]

Main thing folks need to realize as already noted is the shape bulges which is difficult to calculate on paper (the frame and straps will restrict how much, etc.), its not a flat sided box. Ideally if the bag dimensions are listed folks can get a better feel for a bag size regardless of the volume listed (sometimes I wonder if the published volumes for some bags even allow the draw cord to cinch closed...).

Whenever folks reach out to me requesting an "X" volume bag I ask them to specify dimensions instead, I don't work in volume since as noted its difficult to calculate for a bag before hand and also the expectations one person has for a certain volume may or maynot match the next person's expectations based on the variability of user experiences.

 

[Squirrels]

I've found the best way to measure the main compartment of a bag is to drop in a large trash bag and start pouring in pre-measured water by the gallon. Yes, this will yield a volume that absolutely maximizes every single speck of volume, but do it with the bag on the frame and you get at least some standard to compare one bag to the next. A gallon of water is 231 cubic inches.

 

[Mark at EXO]

Our model names only consider the main bag, not external pockets, lid, etc. We do list the actual capacity under Specifications on each pack page. Our 2000 is closer to ~2950, the 3500 is ~4200, the 5500 is ~6800.