Hiking Backpack

Hiking backpacks measured in litres and fitted to a back length

A hiking backpack is sized twice over: once by volume, from small day sacks of around 30 litres up to 75 and 90 litre loads, and once by the length of the wearer's back. The second measurement is the one people skip, and it is the one that decides whether a full sack feels balanced or punishing. The range includes day packs, weekend sizes, women's cuts and coated designs.

How many litres are actually needed?

Volume follows the length of the trip and the bulk of the sleeping kit, not the distance walked. A day on the hill with waterproofs, food and a flask fits inside 30 litres. Around 40 covers a long day with camera gear or a child's spare clothing. Once a tent, a stove and a sleeping bag go in, 50 litres is the realistic floor, and multi-day trips in cold weather push towards 75 and beyond.

Why does back length matter more than the litre figure?

Because the hip belt has to land on the top of the pelvis, not on the ribs or on the thighs. Back length is measured from the bony bump at the base of the neck down to the level of the top of the hip bones, and it has little to do with overall height. Get it right and the weight sits on the skeleton, with the shoulders only steadying the load; get it wrong and everything hangs from the collarbones. Adjustable back systems slide the harness up and down a ladder of anchor points to cover a range of torsos, which is why they are worth having on a large sack.

What should you look at before choosing?

• Hip belt padding: wide, stiffened and long enough to wrap forward past the hip bones rather than stopping at the sides.
• Back ventilation: a tensioned mesh panel keeps the load off the spine and lets air across a sweating back on a climb.
• Access points: a front or side zip saves unpacking the whole sack to reach something at the bottom.
• Lid and hip belt pockets: the places a map, a snack and a phone live so the pack is not opened every hour.

Where should the heavy items go?

Close to the spine and level with the shoulder blades, with soft light items at the bottom and anything needed during the day at the top. Weight carried low or far from the back rotates the load away from the body and forces a forward lean that tires the lower back. A traditional bergen backpack distributes the same load differently by putting side pouches on the flanks, which keeps the centre of the pack narrow.

Will it keep the contents dry?

Rarely on its own. Fabric is coated, but the seams, the zips and the lid are open routes for water in steady rain, and a back panel pressed against a jacket wets through from the outside. A liner or dry bags inside are what actually protect a sleeping bag; a rain cover handles the rest. A waterproof backpack with a roll top closes that gap by design. A heavier duty military backpack answers it with a storm flap over the opening instead.