Backpacking Pack Size: How Many Liters by Trip Length and Season

It’s 9 p.m. the night before you leave. Tent, sleeping bag, sleeping pad, stove, and one fleece too many are spread across the bed, and the 30-liter pack you bought for day hikes won’t close. You push, you cram, you end up sitting on it. No luck: you pick a pack for what it has to swallow, and the number on the tag tells you less than you’d think.

This guide is about backpacking packs, not school bags or carry-ons. It lines up the recommended volumes, explains why one brand’s liters aren’t another’s, then moves on to torso length and weight. It picks up the “night before” step in our guide to your first backcountry camping trip. For what goes inside, see the backcountry camping gear list or, for a day out, the day hike packing list.

How many liters for a day, a weekend, or a week

No official rule sets these volumes, so treat them as ballpark figures. Here are the numbers from Gregory [1], the German brand Deuter [2], and French sporting goods retailer Decathlon [3], three companies that sell these packs, plus the Swiss Council for Accident Prevention (BFU, or BPA in French) [4] and the FFRandonnée, France’s national hiking federation [5]. Read them as advice, each shaped by what its source has in mind.

For a day hike, everyone lands around 20 to 30 liters. The gaps show up once you sleep out. For backcountry camping, Gregory stops at 50 L and Decathlon goes up to 60 L, while Alpkit, a British brand, puts spring-through-fall overnights in its 30 to 45 L packs [6]. Hut trips, common in Europe, are just as unsettled: Deuter talks about 45 to 60 L with meals included, the BFU about a volume barely bigger than a daypack’s, and our guide to the Tour du Mont-Blanc aims for 35 to 45 L. The FFRandonnée, which doesn’t sell packs, settles on 55 L for trips longer than 4 days, possibly with some fold-up stuff sacks [5].

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Winter and summer: what the season changes

For winter, Gregory puts a number on the extra: 10 to 15 L more [1]. Alpkit explains what that space is for, namely extra clothing, crampons, and an emergency shelter, and puts winter daypacks in its 30 to 45 L range [6]. In hot weather, the brand adds, you sometimes need more water: that’s more pounds than liters, and you can work it out with our guide to water and food on a hike.

Why two 35-liter packs don’t hold the same amount

Alpkit says it flat out: nothing guarantees that two 35 L packs have the same capacity, because every brand measures a little differently [6]. There is a standard, though, ASTM F2153, from the American standards organization ASTM International, dated 2007 and reapproved in 2018. It’s sold behind a paywall, and we’re citing only its official summary: it distinguishes an unextended and an extended capacity, and excludes anything not completely enclosed by fabric, such as mesh pockets, water bottle holders, and compression pockets [7]. We didn’t find any ISO or European equivalent.

The idea is easier to see with instructions in hand. CabinZero, a travel bag maker that cites this standard, loosens the straps, then fills the main compartment and all the closed pockets with plastic balls 0.4 to 0.8 in (10 to 20 mm) across, or dried beans, using a 1-liter measuring cup, and counts the cups [8]. Alpkit pours polystyrene beads into a big graduated cylinder, but counts only the main compartment [6]. So on a pack with pockets, the second method gives a smaller number than the first.

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Not everyone follows the standard. Minaal, a travel bag brand that says it applies it, claims many manufacturers skip it, to the point that one company’s 35 L could equal another’s 50 L [9]. That’s a competitor talking, with no measurements to back it up; the takeaway is that the number doesn’t compare from brand to brand.

Then there’s the plus sign. On Deuter’s Aircontact Lite 40+10, the spec sheet lists 40 L [10], and the adjustable top lidThe flap that closes the top of the pack, often with a pocket. Adjustable in height, it frees up room above the main compartment. adds up to 10 L [2]. Compare base volumes with base volumes, and save the extension for resupply days.

Calculating liters: the tape measure lies, adding up helps

The DIY instinct is to multiply height, width, and depth. That works on a moving box. On a pack, here’s what the math gives you using the dimensions manufacturers publish.

The calculation overshoots the listed number by 21 to 49%, and the gap changes from pack to pack: a pack isn’t a box, and nothing lets you work back from its dimensions to its liters. Your own needs add up better. The big items of a backcountry trip have a published packed size, and each is roughly a cylinder.

Spec sheet in inches? Multiply each number by 2.54 to get centimeters, or keep the inches and divide by 61 instead of 1,000. The example below works from the centimeters on three spec sheets. Deuter’s synthetic Orbit +5 sleeping bag is 7.9 in (20 cm) in diameter by 15.4 in (39 cm), or 12 L, a number the spec sheet also gives [16]. Hilleberg’s one-person Akto tent, 17 by 5.1 in (43 by 13 cm), takes up 5.7 L [17], and Sea to Summit’s Ether Light XT pad, 9.4 by 4.3 in (24 by 11 cm), 2.3 L [18]. Total: 20 L. Add that to a 20- to 30-liter daypack and you get 40 to 50 L, right in Gregory’s range, before water and dinner.

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This is an example, not a recommendation: a two-person tent or a different sleeping bag changes the total. But the method takes one evening, a few spec sheets, and a calculator.

Torso length: measure it before you look at liters

Volume tells you what fits; torso length, which Deuter calls back length, tells you whether the pack will carry well. Deuter defines it as the distance between the seventh cervical vertebra and the upper edge of the iliac crestThe top rim of the hip bone, which you can feel under your fingers when you put your hands on your hips. [19]. Gregory walks through the steps on its spec sheets [14]: head tilted forward to find the bump at the base of your neck, hands on your hips sliding up to the top of the bone, then thumbs toward the small of your back, where you read the tape. Decathlon more simply talks about measuring from the waist to the neck vertebrae [3], a lower and less precise reference point.

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Deuter puts its SL packs at around 16.5 in (42 cm), Regular at 18.1 in (46 cm), and EL at 19.7 in (50 cm), give or take 0.8 in (2 cm), and notes that two people of the same height can have different torsos [19]. The measurement is only a starting point: for the brand, trying the pack on is the only sure test [19], and Decathlon recommends trying it loaded [3]. Deuter also sets a threshold on its trekking packs: an adjustable back from 35 L up, which matters most with loads over 22 lb (10 kg) and on long hikes, and none below that, to keep the empty pack light [20].

Size sometimes affects the liters. Deuter adjusts the volume of its EL models [19], and the SL version of the Aircontact Lite lists 35 L instead of 40 L [13, 10]. Gregory, on the other hand, lists 65 L for its Baltoro in both size S and size L, even though the pack goes from 31 to 33 in (79 to 84 cm) tall [14, 15]. One more reason to look at the pack filled rather than at the tag.

How much weight to put in those liters

More liters often means more pounds: the bigger the pack, the FFRandonnée notes, the more we tend to load it [5]. The published limits look alike, but they aren’t equal, and the only U.S. agency figure in the table, from a single national park, runs higher than the rest.

The Spanish study published in January 2026 measured the pressure under the feet of 39 Camino de Santiago hikers, standing and barefoot: compared with no pack, it climbs about 5% with 10% of body weight on board, and nearly 10% with 20% [21]. The authors call this an exploratory benchmark, not a universal safety limit, and their protocol says nothing about injury risk. Michael O’Shea, a physicist at Kansas State University, challenges the fixed percentage from another angle: in his model, strength follows muscle cross-section rather than body weight, so a smaller hiker doesn’t necessarily have to carry less [22]. He himself says the model is too simple to set any one person’s load [22], and finds the idea of a single percentage somewhat misleading [23].

The pack gets a vote too. Deuter recommends 13 to 22 lb (6 to 10 kg) on the Futura 30 SL and 26 to 33 lb (12 to 15 kg) on the Aircontact Lite 40+10 [12, 10], and Gregory 60 lb (27.2 kg) at most on the Baltoro [14]. For Deuter, those numbers are comfort guidelines, not the pack’s strength [20]. Do the math: at 176 lb (80 kg), the FFRandonnée’s 35-lb (16 kg) ceiling already exceeds the 26 to 33 lb Deuter recommends on this 40-liter pack. The empty pack counts too: 1 lb 7 oz (640 g) for the Vaude Agile 20, 3 lb 8 oz (1.59 kg) for the Aircontact Lite 40+10, 4 lb 11 oz (2.13 kg) for the Baltoro in size S [11, 10, 14]. Gregory aims for 70% of the weight on your hips and 30% on your shoulders [1], which is why a hip belt at the right height matters. For kids, see our guide to hiking with kids.

From daypack to overnight pack: which one to get

• You day hike: 20 to 30 L falls within almost every benchmark; go bigger for the mountains or winter.
• You sleep in huts: the numbers run from 35 to 60 L depending on the source; start low, and do a practice pack before you buy bigger.
• One or two nights in a tent: 35 to 50 L, more if your sleeping bag takes up a lot of room.
• A week self-supported: 50 to 70 L, with the FFRandonnée’s 55 L as a reference point.

If you’re only buying one pack, I’d look around 40 L: that’s near the middle of Gregory’s range for tent camping, the top of Alpkit’s, and just above the 35 L where Deuter starts adjusting torso length. Ounce counters, Gregory admits, can get by with fewer liters [1]; I suspect their toothbrushes lost their handles years ago.

The smart move the night before you leave: lay everything out on the bed, do one practice pack, then step on the bathroom scale wearing the pack and subtract your own weight. If it closes without anyone sitting on it and the weight stays under your limit, the volume is right. If not, you don’t necessarily need a new pack: start by evicting that extra fleece.

Worth watching

REI’s Katie and Miranda measure a torso to find the right pack size, then show how to fit the pack: the steps from this guide, in motion.

The video is hosted by YouTube (Google): nothing loads until you play it, and Google may then set cookies.

Guillaume Hoarau

Camping, backpacking, bushcraft and hiking

Guillaume Hoarau writes for Outfarer about camping, backpacking, bushcraft, and hiking. A survival-skills buff and a collector of vintage field manuals, he loves clear explanations, lists that actually help and other people’s stories, which he tells well.

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