Forty-ish liters is a really interesting size for an ultralight backpack. It’s perfect for a fast-and-light overnighter or long weekend, and if your ultralight gear list is really dialed it can serve you well on the longest of long thru hikes.
Personally I’ve straddled the 40 liter line, doing shorter fast and light missions with a ~30 liter pack and longer thru hikes with a roomy but lightweight 60+ liter pack. If I were to add another pack to my collection, it would fall in the ultralight 40 – 50 liter range. While doing my research I came across more options than I expected, but it took some digging. I realized it might be helpful to other hikers if I collected a list of ultralight 40 liter backpacks in one place.
I quickly realized this task is harder than it seems. Every pack maker measures volume and weight differently (Are pockets included? How about the removable hip belt?) and a true apples-to-apples comparison is difficult. I suggest you go look at each pack’s details to understand what you’re really getting, as packs in this class tend to be more configurable than the average backpacking pack. Still, if you’re shopping for an ultralight 40 liter hiking backpack I hope this helps!
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Capacity Considerations
I set out to make a list of ultralight 40 liter backpacks but quickly ran into a problem: there are several different ways to measure pack capacity. The main elements are:
- Main internal pack body
- External pockets
- Extension collar
The most precise specs break out the capacity for every single pocket, while some of the more mass-market packs simply say “40 liters capacity” and leave it at that. I quickly realized that a perfect apples-to-apples comparison is nearly impossible, so I’ve aimed for packs where the main body plus pockets totals between 40 – 50 liters, and the main compartment is at least 30 liters.
Strangely this leaves out some “40 liter” packs, like the Zpacks Arc Haul 40, which has a 28 liter main compartment. Keep this in mind if you’re actually looking for a smaller pack; you might need to look at packs marketed closer to 30 or 35 liters to find a true max capacity of 40 liters. This distinction is important! A pack with a 25 liter main body and 15 liters of pocket space will feel very different from a pack with a 40 liter main body and 10 liters of pocket space, but both packs may be marketed as “40 liter” backpacks. Do your homework to know what size you really need.
Following the lead of several pack makers, I’ve tried to exclude the extension collar capacity from the total where possible. It seems that this volume is meant to be reserved as emergency extra space for that post-resupply afternoon.
There’s also the big question of whether you’ll manage to cram everything inside the pack or strap a bulky item to the outside. Some of these packs have straps at the top or bottom designed to hold a bear canister, accordion-fold sleeping pad, or tent. This is a great way to expand the capacity of a smaller pack, perhaps one you originally chose for shorter excursions, to suit a longer or more involved hike.
Weight Considerations
As a rough rule of thumb, I’ve chosen the “ultralight” threshold to be two pounds and lighter. This rules out some of the more structured packs like those by Granite Gear and the lightest offerings from Osprey. But again, apples to apples comparisons are hard since ultralight packs tend to be more configurable than standard packs.
For example, many of the packs in this list have removable back pads, optional hip belts, and various other bits that can be left at home to shave off a few more grams. They may quote the pack’s weight with or without those bits. Some pack makers (like Zpacks) sell a stripped-down pack and make accessories like shoulder strap pockets available as add-ons, which add on storage space as well as dollars and grams. Others, like MLD, let you configure the pockets when you order. And still others, like Six Moon Designs, give the total weight for the whole package but offer options to slim down.
So as with capacity, you’ll have to look at each pack individually to figure out which configuration suits your needs and exactly how much it will weigh.
Load Capacity Ratings
As you may have guessed by now, these numbers are also a bit subjective. Some manufacturers rate based on the load the pack can carry without risk of damage, some rate based on comfort for the hiker, and some don’t specify. The most configurable packs will have variable load capacity; if you remove the back pad and hip belt you can obviously expect the maximum comfortable load to decrease.
As a general rule though, these are mostly ultralight packs designed for ultralight gear. Many of the manufacturers recommend a base weight of around 12 pounds or less. Though some claim a 40 pound max load, I’d be surprised if this is a “comfort rating” and would suggest most hikers keep their total pack weight below 25 – 30 pounds. If you’re planning to go without a frame or hip belt, aim even lower!
40 Liter Pack Comparison Table
| Pack | Price | Volume (liters, main + pockets) | Weight (oz) | Max Recommended Load (lbs) |
| Volpi UL 40 liters | $220 | 30 + 15 | 14.8 | 33 |
| Atom RE40 | $175 | 35 + 10 | 15.4 | 20 |
| Mountain Laurel Designs Prophet 48L | $325 | 32 + 10 | 17.5 | 25 |
| Alien Outdoor Gear Novum 40 | $200 | 31 + 10 | 19 | 30 |
| Zpacks Arc Haul 50 | $399 | 37 + 13 | 20.8 | 40 |
| Gossamer Gear G4-20 Ultralight 42 | $195 | 30 + 12 | 25 | 30 |
| ULA CDT | $200 | 29 + 21 | 27.1 | 25 |
| Hyperlite Mountain Gear Windrider 2400 | $349 | 40 + 9.8 | 29.8 | 40 |
| Mountainsmith Zerk 40 | $220 | 40 + ? | 30 | 30 |
| Hyperlite Mountain Gear Unbound 40 | $369 | 40 + 9 | 30.1 | 40 |
| Outdoor Vitals Shadowlight 45 | $200 | 35 + 10 | 30.5 | 35 |
| Hyperlite Mountain Gear Southwest 2400 | $349 | 40 + 9.8 | 30.8 | 40 |
| Hyperlite Mountain Gear Junction 2400 | $349 | 40 + 9.8 | 31 | 40 |
| Six Moon Designs Swift V | $250 | 41 + 5 | 36 | 35 |
Fit and Comfort
Though we love to obsess about weight and capacity, obviously there’s more to a pack than its specs. Fit and comfort are possibly the most important factors when wearing a pack day after day. Many of these packs come in multiple sizes, and some have separate size options for hip belts and torso lengths. Some are even adjustable within their size category.
Lastly, shoulder strap style can make a huge difference in both comfort and convenience. Depending on how you like to carry your water while hiking, shoulder strap pockets could be a must-have. Some ultralight packs in this smaller size range are experimenting with vest-style straps inspired by running and fastpacking packs, which can really change the way a pack feels and moves with your body. A few packs, like the Six Moon Designs Swift and ULA CDT, even offer a range of options.
Did I miss your favorite ultralight 40-ish liter pack? Let me know in the comments below.
More Backpacking Resources
If you found this article helpful, you might also like these:
- Easy No-Cook Breakfast Ideas
- Review: Six Moon Designs Haven Tarp
- Thru Hiking the Arizona Trail: Essential Q&A
Or visit the backpacking section for lots more.
About the Author
Hi there, I’m Alissa. I’ve had the pleasure of hiking the Arizona Trail, Colorado Trail, John Muir Trail, Tahoe Rim Trail, and countless shorter amazing trails throughout the US and abroad. I love solitude, big views, and a good lightweight gear setup. Learn more or say hi.
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