Best backpacking backpacks: volume, weight, and torso fit guide

Volume and weight: comparing 40-to-65-liter packs from the makers

For three-season weekend trips, week-long wilderness routes, and long-distance thru-hikes, the 40-to-65-liter bracket is the core capacity range. However, outdoor brands do not all calculate volume the same way. Mainstream manufacturers—including Osprey, Gregory, and REI Co-op—measure liter capacity strictly using enclosed storage (the main compartment plus zippered lid and side pockets), leaving open stretch-mesh pockets out of the stated number. Ultralight and cottage makers frequently state either internal cubic inches or total combined volume including open exterior pockets.

Lightweight ventilated and modular packs (2.6 to 2.9 pounds)

For hikers whose total loaded weight stays at or below 30 to 35 pounds, lightweight internal-frame packs cut more than two pounds of empty weight compared to traditional expedition bags without giving up a load-bearing hip belt or back ventilation:

• Osprey Exos 58: According to Osprey’s Exos 58 specifications, the size S/M provides 58 liters (3,539 cubic inches) at 2.84 pounds (1.288 kilograms), while the size L/XL provides 61 liters (3,722 cubic inches) at 2.94 pounds (1.334 kilograms). A 4-millimeter LightWire alloy perimeter frame tensions an AirSpeed 3D mesh backpanel off your spine, supporting a recommended load range of 30 to 35 pounds (14 to 16 kilograms). Its women-specific counterpart is the Osprey Eja 58.
• REI Co-op Flash 55 Pack: Listed on REI’s Flash 55 product specifications, the men’s model holds 53 liters in Small, 55 liters in Medium, and 57 liters in Large at an empty weight of 2 pounds 12 ounces to 2 pounds 14 ounces (1.25 to 1.30 kilograms). REI lists a spring steel frame and a roll-top lid, and the lid, Packmod hip-belt and shoulder-strap pockets and compression straps are removable to reduce weight.
• Gregory Focal 48: Built for compact three-season kits, Gregory’s Focal 48 specifications list the size Large at 52 liters and 2.76 pounds (1.25 kilograms). It uses a perimeter aluminum frame with a tubular fiberglass anti-barreling cross-stay and FreeFloat dynamic hip-belt panels, rated for a maximum load of 30 pounds (13.6 kilograms). Gregory’s women-specific packs in a similar class are listed in its sizing chart as the Facet 45/55. For a detailed look at how AirSpeed ladder-lock sizing and FreeFloat hipbelt flex panels stack up on the trail, read our Osprey Exos vs Gregory Focal comparison.

Ultralight internal-stay thru-hiking packs (1.9 to 2.4 pounds)

When you pair a compact shelter from our best ultralight tents guide with a compressible sleeping bag and pad, you can step down to an ultralight roll-top pack that eliminates zippered top lids and suspended mesh frames:

• Hyperlite Mountain Gear Southwest 55: As detailed on Hyperlite Mountain Gear’s Southwest page, the pack holds 55 liters inside the main roll-top compartment plus 13.4 liters across solid Hardline with Dyneema exterior pockets (68.4 liters total). Hyperlite lists it at 30.8 ounces (874 grams) in White or 30.9 ounces (876 grams) in Black, made from Dyneema Woven Composite 3.9, using two removable contoured aluminum stays and a quarter-inch foam backpanel pad to support loads up to 40 pounds (most comfortable under 30 to 35 pounds).
• ULA Circuit: According to ULA Equipment’s Circuit specifications, the standard Circuit is listed at 68 liters total, with a 2,400-cubic-inch (39.3-liter) main body and a 500-cubic-inch (8.2-liter) extension collar plus mesh and side pockets. It weighs 38.5 ounces (1,092 grams) and uses a 1.2-ounce carbon fiber and Delrin suspension hoop with a dense internal foam pad and a single aluminum stay to carry up to 35 pounds (15.9 kilograms).

Full-suspension heavy haulers (about 4.7 pounds)

• Osprey Atmos AG 65: When your trip requires carrying a large bear canister, extra cold-weather insulation, or extra water, Osprey’s Atmos AG 65 specifications list 65 liters (3,967 cubic inches) at 4.61 pounds (2.09 kilograms) in size S/M and 68 liters (4,150 cubic inches) at 4.81 pounds (2.18 kilograms) in size L/XL. Its 4-millimeter powder-coated full peripheral frame supports a continuous AntiGravity 3D suspended mesh panel that wraps from the shoulder blades seamlessly into the hip belt, rated for 30-to-40-pound loads and shipped with an integrated raincover. Its women-specific counterpart is the Osprey Aura AG 65.

Torso length fitting: how to measure and size your pack

The single most important rule of backpack fitting is that standing height does not determine pack size. A six-foot-two hiker with long legs can have a 17.5-inch torso that requires a size Small or Medium pack, while a five-foot-five hiker with a long spine can measure 19.5 inches and need a size Large. If a pack’s torso length is too long, the shoulder harness sits above your shoulders and the hip belt slides down off your pelvis; if the torso is too short, the hip belt rides high around your waist and pulls weight down onto your collarbones.

Step-by-step spinal torso measurement

Following REI’s backpack fitting methodology, ask a friend to take two measurements with a flexible cloth tape measure:

1. Find your C7 vertebra (top anchor): Stand up straight and tilt your chin toward your chest. Feel at the base of your neck where your shoulders slope away for the largest, most prominent bony protrusion—the seventh cervical vertebra.
2. Find your iliac crest (bottom anchor): Place both hands firmly on the top shelf of your hip bones on either side of your waist, with your index fingers pointing forward and your thumbs pointing inward toward your spine. Imagine a level horizontal line connecting your two thumbs across your lower back.
3. Measure along the spine: Have your partner hold the top of the tape measure at the C7 vertebra and trace the natural curve of your spine down to the imaginary line between your thumbs. That number in inches (typically between 14 and 22 inches) is your torso length.
4. Measure your hip circumference: Wrap the tape measure around the top ridge of your hip bones (along the iliac crest, slightly higher than where trouser belts sit) to verify that the pack’s hip-belt wings will buckle without bottoming out.

Fixed versus adjustable torso harnesses

Once you know your measurement in inches, compare how different pack families handle torso sizing:

• Adjustable harness yokes: Both the Osprey Exos 58 (Osprey lists 4 inches of torso adjustability), the Osprey Atmos AG 65 (Fit-on-the-Fly shoulder harness and extendable hip-belt pads), and the REI Co-op Flash 55 (REI lists an adjustable torso) let you fine-tune the vertical spacing between the hip belt and shoulder straps within each size.
• Fixed size-specific frames: To save hardware weight, the Gregory Focal 48 (Small 16–18 in., Medium 17–20 in., Large 19–22 in.) and Hyperlite Mountain Gear Southwest 55 (Extra Small, Small 15–17 in., Medium 17–19 in., Large 19–21 in., Tall 21+ in.) use fixed-length harnesses sewn directly into the backpanel. Measuring accurately before ordering a fixed-torso pack is essential.
• Modular custom sizing: ULA Equipment lets buyers select their exact torso size (Small 15–18 in., Medium 18–21 in., Large 21–24 in., X-Large 24+ in.), six independent hip-belt circumference sizes (from 26 inches up to 47+ inches), and either J straps (traditional straight straps, best suited to flat or square shoulders) or S straps (contoured, best suited to standard or sloping shoulders) on the ULA Circuit.

Suspension architectures and backpanel ventilation

How a backpack connects its frame to your back determines both airflow in warm weather and center-of-gravity stability on steep, technical trails.

Tensioned-mesh (trampoline) backpanels

The Osprey Exos 58, Gregory Focal 48, and Osprey Atmos AG 65 suspend a taut, breathable mesh screen over a curved perimeter alloy frame. In the Exos 58 and Focal 48, this creates an open air cavity between your shirt and the nylon pack bag so crosswinds can evaporate sweat continuously on summer climbs. On the Atmos AG 65, the continuous AntiGravity mesh extends into the lumbar pad and hip belt itself, eliminating stiff foam edges against your iliac crest.

Flush foam and internal-stay backpanels

The REI Co-op Flash 55, Hyperlite Mountain Gear Southwest 55, and ULA Circuit place contoured foam pads directly against your back, backed by internal aluminum stays, a carbon-fiber hoop, or a spring-steel wire loop. While a flush backpanel traps more body heat than a suspended mesh screen, it keeps heavy items—such as bear canisters, food bags, and water reservoirs—pressed directly against your spine rather than curved an inch rearward. For step-by-step instructions on balancing heavy core items, fitting a bear canister vertically against the stays, and dialing in your load-lifter straps to a 45-degree angle, read our guide on how to pack a backpack.

Fabrics, closures, and pocket layouts

Modern backpacking packs divide into two distinct design philosophies regarding access and fabrics:

• Recycled high-tenacity nylon with floating lids: The Osprey Exos 58, Osprey Atmos AG 65, Gregory Focal 48, and REI Co-op Flash 55 use recycled ripstop and high-density nylon (Osprey and Gregory list 100D to 210D main fabrics; REI lists recycled ripstop nylon) treated with PFAS-free durable water repellent (DWR). Their floating top lids (brains) provide zippered organization for headlamps, maps, and first-aid supplies from our backpacking checklist, and the Exos, Focal, and Flash all include an integrated under-lid weather flap so you can leave the brain at home to save 4 to 5 ounces.
• Roll-top laminates and high-abrasion weaves: The Hyperlite Mountain Gear Southwest 55 and ULA Circuit omit top lids and excess zippers entirely in favor of a dry-bag-style roll-top collar held down by a top Y-strap or single buckle. As your food volume shrinks over a five-day trip, you simply roll the collar down tighter to eliminate dead air space. You can weigh and compare your full kit before choosing a pack volume using our interactive packing list tool.

How we chose

We don’t test gear ourselves. We choose picks through objective evaluation of published manufacturer technical specifications, suspension frame architectures, fabric denier and laminate ratings, warranty coverage, and verified long-term owner review patterns across major outdoor retailers.

We verify torso sizing matrices, enclosed versus external liter capacities, empty weights across frame sizes, and recommended load ceilings directly from primary brand documentation without accepting paid placements or staging unverified field trials. Read our complete evaluation standards on our how we choose page and review our affiliate disclosure.