By Priya Anand, Backpacking Gear Research Writer · Published September 14, 2026, 6:03 PM ET
Direct Answer
A 35–45L backpack is the right size for a one-night hike for most three-season backpackers, holding a shelter, sleeping bag and pad, a stove, and about a day and a half of food without much unused space. Minimalist or lightweight-leaning packers can size down; hikers with bulkier gear often prefer the upper end of that range.
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In plain English
Backpack sizes are measured in liters, the same unit as a big bottle of soda. A 40-liter pack holds about as much as 40 of those one-liter bottles. For one night outdoors, you need room for a tent, a sleeping bag, a sleeping pad (a thin mattress that keeps the cold ground away), a small stove, some food and a warm layer.
The surprising part is that food takes up little room on a one-night trip. What fills the pack is the bedroom: the tent and the sleeping bag. A fluffy, warm sleeping bag can take up a big share of the pack on its own.
That is why two people on the same overnight trip can need very different packs. One with small, modern gear might fit it all in 35 liters. Another with an older tent and a thick cold-weather bag may need 45 or more.
A 35–45L backpack fits most one-night hikes, carrying a shelter, sleep system, stove or cold-soak setup, one to two days of food, and basic safety gear without leaving much unused volume. The exact number within that range depends more on gear bulk than on the single night itself.
What pushes you toward 35L vs 45L?
A compact sleep system, a lightweight shelter like a single-wall tent or tarp, and a cold-soak or no-cook meal plan all keep total volume needs closer to 30–35L. A bulkier three-season tent, a lower-temperature-rated sleeping bag, a full canister stove setup, or an extra insulating layer for cold nights push the same one-night trip closer to 40–45L. Season matters too: a summer overnight typically needs less bulk than a shoulder-season trip with a warmer bag and extra layers.
How pack size compares by trip length
Trip Length
Typical Volume
What Fills It
1 night
30–45L
Shelter, sleep system, 1–2 days food
2 nights (weekend)
45–55L
Same core kit plus one extra day of food/fuel
3–4 nights
50–60L
Added food volume, possible bear canister
Does a smaller pack mean a worse fit?
Not if torso length is correct. A well-fitted 35L pack, measured from the C7 vertebra to the iliac crest rather than by height, will carry a one-night load more comfortably than an oversized 55–65L pack loaded light, since excess unused volume in a large pack can shift and ride unpredictably even when cinched down. Matching pack size to a single night's actual gear list, rather than buying extra room "just in case," keeps the load closer to the commonly used guideline of staying at or under roughly 20% of body weight for a comfortable carry.
Why published size ranges disagree
This page puts one night at 35 to 45 liters, and its comparison table starts at 30. The Washington Trails Association is more generous: it says a 45 to 50 liter pack should fit the gear for a standard one- or two-night trip, and that 25 to 30 liters is good for a full day hike.1 Neither is wrong. WTA's figure covers up to two nights and a typical three-season kit, while this page's range assumes one night and a fairly compact kit. If you are building a first kit from borrowed or older gear, the WTA number is the safer starting point.
Liters are not always counted the same way, either. Gossamer Gear, for example, lists its Mariposa 60 as 36 liters in the main body plus 24 liters across seven exterior pockets.5 A pack whose volume sits largely in outside pockets holds a bulky sleeping bag differently from one with a single big main compartment, so compare main-body volume where you can.
The sleep system sets the size
Warmth is where bulk comes from. Sleeping bag ratings follow the EN/ISO system, where the comfort rating is the temperature at which an average woman sleeps comfortably without curling up, and the limit rating is where an average man stays in thermal balance while curled up.6 The extreme rating is a survival figure where hypothermia is possible, not a target.7 Choosing a bag by its comfort rating usually means more loft, and more liters, than choosing by the limit.
The pad matters just as much. Big Agnes suggests an R-value of 4 to 4.8 from spring through fall, because shoulder seasons still bring cold nights, and 2 or lower only for summer or very warm weather.8 A warmer pad may pack larger, which is one more reason a shoulder-season overnight lands at the top of the range.
When one night needs a canister
Food-storage rules can add volume that no amount of clever packing removes. Rocky Mountain National Park requires bear canisters for all wilderness overnights and asks you to show one to get your permit,2 and New York's Eastern High Peaks Wilderness requires them for overnight campers from April 1 to November 30.3 Typical canisters measure about 8 by 12 inches and hold up to five days of food, far more than one night needs, so the canister's shape, not your food, sets the space.3 Rules are park-specific and change, so check your destination's current page before choosing a pack.
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