In plain English
A week-long hike means about six or seven nights sleeping outdoors and carrying everything you need. That includes a tent, a sleeping bag, a mat to sleep on, a small stove, clothes, and a week's worth of food.
Backpacks are measured in liters, just like drink bottles. A 70-liter pack is big, about the size of a medium checked suitcase, only shaped to sit on your back. Your gear takes about the same space on any trip; it's the food that grows with every extra day.
If your gear is small and light, or you can pick up more food halfway, a smaller pack can work. If it's cold, or you have to carry a hard plastic food container to keep bears out, you'll want a bigger one.
A week-long hike typically needs a 65- to 75-liter backpack, since a base gear list of shelter, sleeping bag, pad and cook kit gets combined with roughly six to seven days of food and fuel that has to fit alongside it. That range assumes a standard three-season kit; a bear canister, extra cold-weather layers or a bulkier sleeping bag push the same trip toward 75 to 80 liters instead.
Food is the biggest swing factor over a week. Budgeting roughly 1.5 to 2.5 liters of pack space per day of food is a common planning estimate that tends to overshoot for compact, dehydrated meals, so treat the 10 to 17.5 liters it gives for a full week as a ceiling on top of base gear.
What affects where in the 65–75L range to land?
- Resupply plans: a mid-trip resupply lowers the food volume actually carried at any one time, letting some hikers use a smaller pack than a fully self-supported week would need
- Base weight: an experienced ultralight hiker can often complete the same week in 50 to 60 liters using more compressible, lighter individual items
- Season: winter and shoulder-season trips need extra insulation volume on top of the standard range
- Wildlife regulations: a required bear canister adds a fixed volume block regardless of how everything else is packed
New backpackers planning a first week-long trip are generally better served sizing toward the upper end of the 65-to-75-liter range, since a pack with some spare room is easier to live with than one that requires gear lashed to the outside.
Why published ranges for a week disagree
There's no standard for sizing packs by trip length, so figures differ. This page suggests 65 to 75 liters for a week, while the Washington Trails Association says a 50 to 70 liter pack suits trips of 3 to 7 nights and calls 70-plus liters a large pack for carrying a lot of gear and food.1 Makers frame their own packs differently too. Osprey positions the Atmos AG 65 for heavyweight weekends or week-long trips,2 while Kelty positions its Asher 65 for 2 to 3 days in the backcountry.3 The same 65 liters is a weekend pack to one brand and a week pack to another, which shows how much depends on the kit going inside.
Headline liters are also counted differently. Gossamer Gear lists its Mariposa 60 as 60 liters in total, with 36 in the main body and 24 across seven outside pockets.4 When a food canister or a bulky sleeping bag has to fit inside, compare main-compartment volume rather than the total.
Base weight: the biggest lever
Base weight is the weight of all your gear minus consumables such as food, water and fuel.5 Gossamer Gear's categories put lightweight backpacking under 20 pounds, ultralight under 10 and superultralight under 5.6 The Appalachian Trail Conservancy notes that the pack, shelter and sleeping bag, the 'big three', are usually the heaviest pieces of gear,5 and they are usually the bulkiest too, so that's where a smaller-pack plan starts.
The page's point that experienced ultralight hikers can manage a week in 50 to 60 liters fits that picture, but the pack's load rating then becomes the limit. ULA gives its 55-liter Ohm a 30 lb max load,7 and Gossamer Gear rates the Mariposa 60 at a 30 lb comfort load and 35 lb max.4 A week of food added to even a light base kit can approach those numbers, so a smaller pack only works if both the volume and the weight fit.
Season changes the kit, not just the clothes
Colder nights mean bulkier sleep gear. Big Agnes suggests a sleeping pad R-value of 2 or lower for summer, 4 to 4.8 for spring through fall because shoulder seasons still bring cold nights, and 5 or higher for snow or frozen ground.8 Warmer pads tend to be thicker or heavier, and warmer sleeping bags take more room, which is why the page pushes cold-season weeks toward the top of its range.
Stove choice shifts too. MSR says liquid-fuel stoves generally perform best in cold conditions, while canister stoves are almost always lighter and more compact.9 It also notes that canister pressure falls as temperatures drop and the user can't offset it.10 A cold-weather week may need a bulkier liquid-fuel setup plus more fuel, one more reason winter trips land above a three-season range.
