What Size Backpack Do I Need for a Weekend Trip?
For a 1-3 night trip in mild 3-season weather, 40-50 liters covers most adults with a reasonable shared or lightweight gear list. Bulkier gear — a heavier tent, a cold-rated bag, a bear canister — can push that toward 50-65 liters even for a short trip. Bigger isn't automatically better.
The one thing to know: Backpack volume (liters) should be sized to trip length and season, not maximized: a rough guide is 20-35L for a day hike, 40-50L for a 1-3 night trip in mild weather, 50-65L for a 3-5 night trip or a shoulder-season trip needing bulkier gear, and 65L+ for winter trips or multi-day trips needing a bear canister and heavy cold-weather gear. Buying a bigger pack than your trip needs tends to result in genuinely overpacking, since most people fill whatever volume they're given rather than packing a fixed gear list.
Why oversizing backfires
Most people fill whatever volume they're given rather than packing a fixed gear list — so a 65L pack bought "to be safe" for a weekend trip tends to result in genuinely overpacking, more weight on your back, and a bulkier, less balanced load than a correctly sized 40-50L pack carrying the same trip's actual gear.
Fit is about torso length, not height
Backpack fit is measured by torso length — the distance from your C7 vertebra (base of neck) to your iliac crest (top of hip bones) — not your overall height. Most quality packs list an adjustable torso range or come in fixed S/M/L sizes matched to torso length; an outfitter fitting or the brand's published torso-measurement guide is far more reliable than guessing from height alone.
Picks by trip size
Research-based picks (how we evaluate), from published specs, not hands-on lab tests. Live Amazon search links, no prices or ratings, an honest drawback on each.
Osprey Osprey Atmos AG 65
65L, Anti-Gravity suspended mesh back panel, adjustable torso length, ~4.5 lb
The Anti-Gravity suspended mesh back panel is a genuinely different ventilation/load-transfer design from a standard foam back panel, noticeable on long, hot climbs.
Best for: 3-5 night backpacking trips carrying a full sleep system, shelter, and food
Watch out: 65L invites overpacking — most people fill whatever volume they're given, so the pack itself won't force better gear discipline; weigh your loaded pack, don't just fill the bag.
Check price on AmazonGregory Gregory Baltoro 65
65L, adjustable torso + hip belt sizing, dedicated hip-belt pockets, ~5 lb
Highly adjustable torso and hip-belt fit system that accommodates a wider range of body shapes than many fixed-frame competitors.
Best for: Multi-day trips for hikers who need precise fit adjustment for a heavy load
Watch out: It's on the heavier end of the 60-70L class — if base pack weight matters to you, this trades some ounces for its adjustability and load-hauling comfort.
Check price on AmazonREI Co-op REI Co-op Trail 40
40L, internal frame, adjustable torso, ~3.3 lb
A 40L internal-frame pack sized correctly for 1-3 night trips instead of an oversized 65L that tempts overpacking for a short trip.
Best for: Overnight to 3-night trips, or minimalist multi-day trips with a dialed-in gear list
Watch out: 40L is genuinely tight if you're carrying winter gear or bulky non-compressible items (a big tent, bear canister, and cold bag together can max it out fast).
Check price on AmazonOsprey Osprey Daylite Plus
20L daypack, hydration-compatible, hip fin stabilizer straps, ~1.6 lb
A genuine daypack sizing (20L) for actual day hikes out of a basecamp, rather than an underfilled overnight pack doing double duty.
Best for: Day hikes from a car-camping or basecamp setup
Watch out: No internal frame and minimal suspension — fine for a day's worth of water/snacks/layers, but not built to comfortably carry serious overnight weight.
Check price on AmazonThis page is general gear-spec information, not a substitute for an in-store or outfitter fit check.
Frequently Asked Questions
For a 1-3 night trip in mild 3-season weather, 40-50 liters is the typical range for most adults carrying a shared or lightweight gear list. Bulkier gear (a heavier tent, cold-weather sleeping bag, or bear canister) can push that need toward 50-65 liters even for a short trip.
No — buying more liters than your trip needs tends to result in genuinely overpacking, since most people fill whatever volume they're given rather than sticking to a fixed gear list. A properly sized pack forces better gear discipline and is also lighter and more comfortable when not stuffed to capacity.
Backpack fit is based on torso length (the distance from your C7 vertebra to your iliac crest), not your height — most quality packs list an adjustable torso range or come in fixed S/M/L sizes matched to torso length. An outfitter fitting or the brand's published torso-measurement guide is more reliable than guessing from your height or shirt size.
Internal frame packs (the modern standard) use frame stays or a framesheet inside the pack body for a closer center of gravity and better mobility on uneven terrain. External frame packs expose a rigid frame outside the pack body, which can carry very heavy or oddly shaped loads well but rides higher and less agile — now mostly a niche or specialty choice.
A dedicated rain cover or a pack liner (a large trash-compactor bag lining the main compartment) protects gear from rain, since most backpack fabrics are only water-resistant, not fully waterproof, especially at seams and zippers. A liner is generally more reliable than a cover alone, since a cover can't protect the parts of the pack pressed against your back.