By Priya Anand, Backpacking Gear Research Writer · Published September 14, 2026, 6:03 PM ET
Direct Answer
A 3-day hike, meaning two nights on trail, typically calls for a 45L to 60L backpacking backpack depending on season and gear list. Efficient three-season packers often fit two nights into 45–50L, while a bulkier sleeping bag, cold-weather layers, or shared gear pushes that toward 55–60L.
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In plain English
A three-day hike usually means two nights sleeping outside. You walk in on day one and camp, walk all of day two and camp again, then walk out on day three. So you pack the same bedroom gear as for one night, plus a bit more food.
Food turns out to be the smaller part of the jump. The things that change pack size most are how warm your sleeping bag is, whether you share a tent with a friend, and how much water the trail forces you to carry between streams.
There is also a second size that matters as much as liters: the pack's back length. Packs come in sizes that match the length of your back, not how tall you are. A pack in the right back size lets the weight rest on your hips, so the whole trip feels easier.
A 3-day hike, meaning two nights on trail, typically calls for a 45L to 60L backpacking backpack depending on season and gear list. That range assumes a standard three-season kit: a tent or shared shelter, a 20°F to 30°F sleeping bag, a sleeping pad, a stove and cook system, and food and water for two nights.
What determines where in that range you land?
Packing style is the main variable. Efficient packers with a moderate, non-ultralight kit typically fit two nights comfortably into 45–50L. Hikers carrying a bulkier winter-leaning sleeping bag, extra layers for cold or wet conditions, or a larger share of group gear like a two-person tent often need closer to 55–60L for the same two nights.
How food weight factors in
Food adds roughly 1.5 to 2.5 lbs per person per day, so a 3-day hike typically means 3 to 5 lbs of food, a modest but real chunk of both weight and volume compared to a single-night trip. That's part of why a 3-day hike generally needs noticeably more capacity than a one-night trip, even though it's only one extra night of gear.
Quick reference by trip style
Packing Style
Typical Capacity for 2 Nights
Ultralight, minimal kit
40–50L
Standard 3-season kit
45–55L
Bulkier or cold-weather kit
55–60L
Getting the size right
Capacity is only half the equation; torso length, measured from the C7 vertebra to the iliac crest, decides whether a pack fits regardless of its liter count. A 50L pack in the wrong torso length will ride worse than a well-fitted 45L pack, so check size charts against your own measurement before choosing a liter number for a 3-day trip.
What the food rule of thumb can and can't tell you
The 1.5 to 2.5 pounds per person per day on this page is a hiking-community convention rather than a published standard, and nothing in this site's verified sources backs a specific per-day food weight. What research does offer is energy use. The Compendium of Physical Activities rates backpacking at 7.0 METs, where one MET is about 1 kcal per kilogram of body weight per hour.4,5 For a 70 kg (154 lb) hiker, six hours of backpacking works out to roughly 2,900 kcal for the walking alone, before camp chores and sleep.
There is also a ceiling on what you can replace. Research on extreme endurance events found the body's digestive energy supply tops out around 2.5 times basal metabolic rate, and spending beyond that draws down body stores.6 On hard trail days you will likely burn more than you eat, so extra food past what you can realistically eat just adds weight.
Water and the two-night math
Water swings pack weight more than food does. A liter weighs about a kilogram,7 and in a dry park the totals get large fast: the NPS at Guadalupe Mountains asks backpackers to carry a gallon per person per day, at about 8 pounds a gallon, which means roughly 24 pounds of water for a three-day, two-night trip.2 On a trail with reliable streams you might carry two liters at a time and treat water as you go; the CDC notes that boiling, filters and chemicals each have limits, and that most portable filters do not remove viruses or bacteria.8
That is why the 45 to 60 liter range here is best read as a volume range for a kit with regular water sources. A desert route with long dry stretches needs both extra space and a frame rated for the weight. REI, for example, rates its Traverse 60 for loads up to 45 pounds,9 while it describes its lighter Flash 55 as comfortable up to 35 pounds.10
Reading a 20°F or 30°F sleeping bag label
The page assumes a 20°F to 30°F bag, which is a reasonable three-season choice, but the number on the label needs reading carefully. Under the EN/ISO system the comfort rating reflects an average woman sleeping relaxed, the limit rating is where an average man stays in thermal balance while curled up, and the extreme rating marks serious hypothermia risk and is not a target.11 A bag sold as 20°F on its limit rating will feel colder than one rated 20°F for comfort, and the warmer bag usually packs bigger, pushing you toward 55 to 60 liters.
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