By Priya Anand, Backpacking Gear Research Writer · Published September 14, 2026, 6:03 PM ET · Updated September 29, 2026, 6:16 PM ET
Direct Answer
Many thru-hikers use a 45- to 65-liter pack, with the right size set by the trail's longest food carry rather than total distance: town-dense trails like most of the Appalachian Trail fit toward the low end, while remote trails like the Continental Divide Trail or bear-canister routes like the John Muir Trail push toward 60 liters or more.
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In plain English
A thru-hike means walking an entire long trail from one end to the other, often over several months. Nobody can carry months of food, so thru-hikers walk into towns every few days to buy more. That's called resupplying.
Because of that, the size of backpack you need depends mostly on the longest gap between towns. If the next shop is three days away, you carry three days of food. If it's eight days away, you carry eight, and that needs a much bigger bag. Your tent, sleeping bag and clothes take up about the same room either way.
Pack size is measured in liters, like a drink bottle. A 50-liter pack holds about as much as 25 large two-liter soda bottles. Most thru-hikers pick something in the middle and keep their gear light, so the pack stays comfortable for months.
Pack size for a thru-hike depends far more on the longest stretch of food a hiker carries between resupply points than on the trail's total mileage. A trail with towns every three to four days needs less capacity than one with six- to nine-day carries, even if the second trail is shorter overall.
A useful starting guideline: budget roughly 30 to 40 liters for a three-season sleep system, shelter, clothing, and cook kit, then add roughly 1.5 to 2.5 liters of additional capacity for each day of food carried beyond a base three- to four-day resupply cycle.
That guideline plays out differently across the major U.S. long trails:
Appalachian Trail hikers commonly use 45 to 65 liters, since most resupply carries run three to five days, with Maine's 100-Mile Wilderness as the main exception.
Pacific Crest Trail hikers commonly use 40 to 70 liters (ULA says its 68-liter Circuit has been the most popular PCT pack for four years), reflecting the trail's graded tread and lighter average kit, though a Sierra Nevada bear canister adds several liters through that stretch.
Continental Divide Trail hikers commonly use 55 to 65 liters or more, driven by the trail's longest average carries and heavier navigation gear.
John Muir Trail hikers commonly use 50 to 65 liters, driven by a mandatory bear canister and sparse resupply points across roughly 210 miles.
A common rule of thumb keeps total pack weight, food and water included, near 20% of a hiker's body weight, and a correctly fitted hipbelt, sized from an accurate torso measurement, is meant to carry most of that load rather than the shoulders.
What the 20% rule is really based on
Some guides say total pack weight is generally kept close to 20% of body weight. That figure is widely repeated among hikers, but no primary study sets it, so treat it as a community rule of thumb rather than science. The evidence is more varied. Deuter states people can carry a maximum of 20 to 25% of their body weight.1 A 2022 review of backpack ergonomics says adult loads in military, hiking and mountaineering settings should generally not exceed 40% of body mass.2 And a 2026 study of long-distance hikers found foot pressure rose clearly once packs passed about 10% of body weight.3
Real thru-hikers don't match the 20% figure either. In a study of Appalachian Trail long-distance backpackers, packs averaged 25.0% of body weight for men and 27.9% for women.4 The useful takeaway is the direction, not a magic number: lighter is easier on feet and joints over months, and the heaviest days come right after the longest resupply.
How much does the hip belt really carry?
Some guides say a fitted hip belt carries roughly 80% of the load. Sources disagree. Big Agnes aims for about 80% on the hips,5 and the Washington Trails Association gives the same figure,6 while Alpkit gives a range of 60 to 80%.7 US Army doctrine, describing framed packs with hip belts carrying 31 to 90 lb, puts it at about 30% on the hips and lower back and 70% on the shoulders.8
What the sources agree on is the direction. A study of load-carriage discomfort found the hip region tolerates pack pressure significantly better than the shoulders and recommended shifting load to the hips wherever possible.9 For a thru-hiker, that makes torso fit and a well-sized hip belt more important than a few liters of capacity either way.
Bear canisters, food volume and label liters
Where canisters are required, they set a hard floor on capacity, and the rules are a patchwork. In Sequoia and Kings Canyon, containers are required May 1 to October 31 in named areas such as the Rae Lakes Loop and Dusy Basin, and highly recommended throughout both parks.10 Hanging food is illegal everywhere in Yosemite,11 and Inyo National Forest food storage rules apply year-round in all its wilderness areas.12
Canisters also give a rough check on the page's estimate of 1.5 to 2.5 liters of pack space per day of food, which is itself a planning rule of thumb. Glacier Bay's loaner canister holds 560 cubic inches, about 9 liters, and is rated for about six days of food for one person,13 or roughly 1.5 liters a day for densely packed food. Bulky, loosely packed food takes more.
Label volume needs care too. ULA says its 68-liter Circuit has been the most popular Pacific Crest Trail pack for four years, citing a hiker survey,14 which is larger than the 40 to 55 liters some guides give for the PCT. Part of the gap is how liters are counted: Gossamer Gear lists its Mariposa 60 as 60 liters in total, with 36 in the main body and 24 across seven outside pockets.15
