Sizing a McHale pack: pack circumference and pack fit

Which pack model are you planning to get? If you want a 68L internal volume I would be looking at getting the P&G bayonets which are extension stays that lengthen the frame  from from 23″ to about 29″ and the pass through harness.

If so, this example on the page is a start and adjust from there:

Just pull your packs circumference from the chart above and multiply it by whatever height number you want. Our LBP 36 (36″ circumference) to the top of say the shouldern height section of the main frame, a 23″ frame is; 23 x 103 = 2369 cuin. It’s maximum bag height would be about 40″. That’s; 40 x 103=4120 cuin. But, that leaves no bag to draw up with the drawstring. A 30″ height is more reasonable; 30 x 103=3090 cuin. The P&G Bayonets typically add 5″ and 6″ for large volume packs. Let’s just add 6″ to that 23″ frame and we get 29″ of course. Volume to the top of the bayonets is then 29″ x 103″ = 2987 cuin.

My pack is an S-Sarc and it is 39″ at the bottom and 42 or 44 at the top and is about 42 inches tall. I can measure the width and depth to give you an idea of the pack dimensions. It’s probably in the 80-85L range.

I think the standard frame height is 23″ so you can pick a circumference to determine the volume at the top of the frame and also with the bayonet installed.

If you are looking for something similar in size to the Circuit, it is not 68L. ULA is delusional about the capacity of the pockets to claim it is 68L. They claim the side pockets are almost 7 liters which is wildly inaccurate. Internal volume is around 48L with the collar.

Also, know that the pack is not going to be ultra light. It is going to weigh a couple pounds more than the lightest comparable capacity pack. My pack completely stripped no add-on pockets or compression straps is about 4.5 pounds. It more than makes uo for the extra weight in comfort and carrying capacity.  My pack is mostly Challenge Ultra 200TX  which is Ultra 200x with an additional polyester liner inside.

Here is a detailed review that might help give you an idea for sizing: https://popupbackpacker.com/mchale-backpacks-long-term-review-bump-32-and-little-big-pack-36/

Thank you, Bob. Yes,that review is excellent—the best that I’ve found.

I’m looking for a pack that is larger (and carries better) than my ULA Circuit. I’m thinking of a large LBP or a small S-Sarc.

I know how to compute pack circumference and pack volume. My concern is about pack fit: how will I know whether a pack is too wide or too tall to fit well? For example, I can get a 68 L capacity in the main compartment by ordering a pack that has a 50″ circumference and a 21″ height—but I suspect that a 50″ circumference would be too wide for comfort. By contrast, my Circuit’s circumference ranges from 32.5″ to 38″, and I’ve never thought that these measurements were problematic.

I can also get a 68 L circumference by ordering a pack that has a 37″ circumference and a 38″ height. These measurements seem more reasonable. But is a pack that’s  38″ tall (with the bayonets extended) too tall for comfort? How would one know?

This process (paper bag prototyping) won’t tell you how it will carry a load, but it will give you.a good sense of the dimensions relative to your body:

https://backpackinglight.com/forums/topic/59291/

Here are photos of my pack: https://imgur.com/a/uSxNDSt

My pack is 39″ at the bottom, 44″ circumference at the top and 42″ tall. A Weekender Bearikade just fits in the bottom. The Bearikade is 10.5″ tall and 9″ diameter. There is a small bit of space on each end of the bear can, maybe an inch or so. Some other dimensions: back pad is 12″ wide, 23″ from bottom to where the shoulder straps attach to the pack, 29″ to the top of the bayonets (frame extensions). The main frame stays have a one-inch extension so the frame can be shortened to 22″.  I have about a 21.5 or 22″ torso and am 6’4″. With the bayonets installed the bayonets are about mid-ear or a little above on me. The pack can be compressed fairly small including the bottom of the pack.

McHale will send a pack to you to try on for fitting so you will have a good idea of the size of pack you are getting.

Check Superior Wilderness Designs website. They have a 70L pack with circumference dimensions you might be able work off as well.

I don’t own McHale packs…but, in general, it seems you want a pack that can hold a bear can inside comfortably – Bearikade can’s need more circumference than BV500’s. I think a circumference of 38-40 or more is required for a Bearikade to be comfortable. As long as there are compression straps to reduce the circumference when you are not carrying a bear can, then the load can be brought close to your back.

My reference point is HMG backpacks. HMG 55 or 3400 has a bottom circumference of 33.5 and it definitely doesn’t fit my Bearikade Blazer above sleeping bag…it can fit higher up but still not very comfortable. HMG 70 which has a bottom circumference of 37.5 inches works very well….so at least 38 to 40 will be good is what I feel.  With BV500, it can be slightly lesser.

If you don’t care about fitting a bear can inside the bag or if you carry it on top – then it may not matter again.

I have a Sarc-Chasm, a 41” cylinder. A bearikade weekender fits easily without stressing anything. I am 6’2”, 180 lbs and the pack circumference of 41” is well balanced, probably +/- a couple inches in circumference would work as well. Seems to me 50” might prove a bit unwieldy.

As mentioned it will not be an ultralight pack, but will carry well AND last forever. (Just enjoyed my 19th summer)

If you want the volume, use the bayonets.  I’ve carried 2 bear cans on long hauls, in this case the extra height is more useful than additional circumference.

Considering getting another without the bayonets for when I don’t need the volume.

That might be the best name for a pack, ever: McHale SARC-Chasm.

Nice. :)

Bob, Greg, Murali, Steve—thank you to all of you. All of your comments were helpful.

I’m interested in your ideas about pack height. Specifically, at what level does a pack’s height start to cause problems for you? I am imagining, for example, that a pack whose top is higher than your head might cause difficulty with bushwhacking.

Bob, I gather that McHale now defaults to packs that don’t taper. Why did you get yours tapered? (I don’t have a good sense of when tapering is warranted.)

Greg, paper-bag prototyping seems ingenious to me. Among other things, I may use it when I make a bag of my own, which I expect to do at some point.

I prefer a narrow pack for bushwhacking. A taller pack is really only a hindrance if I’m crawling under something and then only briefly. In many ways, i personally prefer a wider pack. With lightweight equipment and careful packing, weight distribution becomes a mute point. My SWD 95 liter is 43″ at the bottom and can be adjusted with compression straps. Much depends on your gear and how it fits. I like to fill up a bag above the stays for less stress at the point where it folds. If that’s not practical, I use a smaller pack. I’ve never filled up a 70 liter pack, but then I have my awkward fitting tent and folding pad on the outside.

I dislike tall packs. They can be cumbersome and affect the center of gravity if not carefully packed. Also, I want room so my wide-brimmed hats don’t interfere with the pack.

Above are pictures of my LBP 36. I’m 5’11 and weigh around 150 lb. The pack isn’t that wide on my skinny body. The extension collar is around 10″ without the P&G extension frame and about 5″ above the end of the P&G extension frame. In both pictures I have rolled the extension collar so it is about level with the frame stays.

I have three McHale packs: LBP 36, LBP 34 and a Bump 32. All have the same size lumbar pad/hip belt connection (about 8″ wide for the pad). I don’t know if the lumbar pad is sized to a person’s measurements or if all are 8″ wide. Keep in mind that the shoulder strap spacing will be made to your measurements, so circumference won’t matter as far as fit goes. Also the packs will feel very secure against your body.

Assuming the contents will be packed as a cylinder shape . . .

32″ circumference ~ 10″ diameter

36″ circumference ~ 11.5″ diameter

40″ circumference ~ 12.75″ diameter

So my preference would be a larger circumference not taller. Get the P&G extensions, they’re awesome.

Terran and Nick, thank you—these posts are helpful. Nick, I especially like your point about pack height affecting the center of gravity.

Nick, thank you too for your great review of your McHale packs. (A link to your review appears near the top of this thread.) I know that I’m not the only one who’s been helped by that review.

Nick, when you wrote your review in 2020, you didn’t mention your LBP 34. Why did you get one, given that you already had two McHale packs? And has any of your thinking about McHale packs—for example, about optional add-ons—changed since 2020?

John,

I got the 3rd pack around 5 years ago. I guess it was an impulse thing. Plus Dan might retire someday and it would be a good back up — I’m 75 and Dan is a year or two younger.

Not a single thing about what I wrote in my review has changed. Everything works as designed, and works well.

I’m 6’1″ 170 lbs and mine is 42/43″ circ with 28″ frames and a total height before rolling the top of 38″. No taper. I was not fitted by Dan as I got it on eBay.

It fits a Bearikade Blazer horizontally all the way to the bottom, which is what I prefer as I need a low center of gravity to feel right moving along

It is very comfy and ideal for my size. Wouldn’t change anything. I am mostly doing rugged trips with as little trail miles as possible and this pack is neither too tall nor too fat for talus, scrambling, bushwhacking, what not.

I like it a lot, but recently got a hold of a 17″ Bearikade for 2 week+ trips without resupply. This canister is huge so I had to switch to another style pack.