Ultimate Direction Fastpack 30 Hydration Pack Patent-pending Infiknit harness is a continuous, seamless back panel and shoulder strap system to prevent abrasion and discomfort. Large, main roll-top compartment expands from 20L to 30L Rear stretch-mesh pocket with low-profile daisy chain system. Water bottle compatible front pockets also fold flat to store other items Dual adjustable sternum straps and side straps for stability and fit. Integrated side compression Z-straps for varying load capacities Removable foam back panel for comfort. Capacity: 20L - 31L / 1220 - 1892 cubic inches. Weight: 24.8 oz / 700g. Dimensions: 24.4" x 11.4" x 10.4" / 62 cm x 29 cm x 26.5 cm. This size qualifies as a "Carry-on bag under airline carry-on rules Sizing at Chest (Unisex): S/M: 24" - 40" / 58 cm - 91 cm. M/L: 32" - 46" / 81 cm - 112 cm. Measure wearing the clothes you intend to wear. A pack full of gear will fit smaller