Backpacks

Direct Answer

Technical backpacking packs are categorized by internal volume in liters (Daypacks: 15–30 L, Weekend Packs: 40–55 L, Multi-Day Trekking: 60–75 L, Expedition: 80–110 L) and sized strictly by Torso Length (measured from the C7 cervical vertebra to the Iliac Crest across the top of the hip bones). Proper suspension systems transfer 70–80% of total pack weight directly onto the pelvic iliac crest via a padded lumbar hipbelt.

Source: ASTM F2153 (Standard Test Method for Measurement of Backpack Capacity) / Outdoor Industry Sizing Standards · Last reviewed Aug 28, 2026

Specs

Daypack Volume Range	15.0–30.0 liters (0.5–1.0 cu ft / 1-day hikes)
Weekend Pack Volume Range	40.0–55.0 liters (1.4–1.9 cu ft / 2–3 day trips)
Multi-Day Trekking Volume	60.0–75.0 liters (2.1–2.6 cu ft / 4–7 day backcountry expeditions)
Expedition Pack Volume	80.0–110.0+ liters (heavy alpine & winter mountaineering)
Torso Length Measurement Datum	C7 Vertebra (neck base) to Iliac Crest (hip shelf) Anatomical Standard
Small (S) Torso Range	38.0–43.0 cm (15.0–17.0 in)
Medium (M) Torso Range	43.0–48.0 cm (17.0–19.0 in)
Large (L) Torso Range	48.0–53.0+ cm (19.0–21.0+ in)
Target Weight Distribution	75–80% on Iliac Crest / 20–25% on Shoulders Internal Frame Transfer
Load Lifter Strap Angle	45.0 degrees angle between shoulder harness and frame top

C7-to-Iliac Crest Measurement & Internal Frame Physics

Torso Measurement Protocol: The user tilts their head forward to locate the prominent bony bump at the base of the neck (the C7 vertebra). Sizing tape runs down the contour of the spine to the horizontal line connecting the top shelves of the hip bones (the iliac crest).
Load Lifters & Peripheral Frame: Internal aluminum stays or HDPE framesheets channel pack mass directly to the lumbar pad and conical hipbelt. Load lifter straps anchored at a 45-degree angle pull the top of the pack close to the upper torso to eliminate rearward gravitational lever torque.