Why fit beats litres every time

Walk into any outdoor shop and you will see rucksacks lined up like a row of suitcases, each with a number stamped on it: 40, 50, 65. It is tempting to think that choosing one is simply a matter of picking the capacity that matches the trip. But any experienced hillwalker will tell you the same thing. A 50-litre pack that fits you properly will carry more comfortably than a 45-litre pack that does not, and the difference becomes obvious around the third hour of a long ascent.

For weekend backpacking in the UK, most people settle somewhere between 45 and 65 litres. That range covers a night or two out in the hills, whether you are wild camping in the Lakes, staying at a bothy in the Cairngorms or doing a low-level trail with a tent. But before you commit to a size, spend your time on fit. It is the single most useful thing you can do.

Start with back length, not shoulder width

The measurement that matters most is your back length, which runs from the base of your neck, roughly the bump at the top of your spine, down to the top of your hip bones. Rucksack manufacturers build their packs around this measurement, usually in two or three sizes. Shoulder straps adjust for width, but they do not fix a pack that is the wrong length.

If the pack is too short, the weight sits high and pulls you backwards. Too long and the hip belt will not sit on your hips at all, which means your shoulders take the load instead. Most decent packs let you move the shoulder harness up or down on a Velcro or ladder adjustment, so get that set before you touch anything else.

• Measure your back length with a tape measure, or ask a shop assistant to do it.
• Set the harness so the hip belt wraps over the top of your hip bones, not your waist.
• Check that the shoulder straps curve over your shoulders without digging into your neck or armpits.

Load transfer: the skill most people skip

Here is the principle worth understanding. A well-adjusted rucksack puts around 70 to 80 per cent of the weight onto your hips, and the rest on your shoulders. Your hips are built for carrying; your shoulders are not. If you finish a day with aching shoulders and a numb neck, the odds are that your hip belt was too loose or sitting in the wrong place.

Do up the hip belt first, cinching it firmly so the padded sections press against the front of your hips. Then tighten the shoulder straps, but not so much that they take the load. Next, pull the load-lifter straps, the small ones at the top of the shoulders that angle up towards the pack. These pull the top of the sack in towards your back and stop it sagging away from you. Finally, snug the sternum strap across your chest to stop the shoulder straps drifting outwards.

Load the pack with the weight you actually plan to carry, then walk up and down a slope or a set of stairs for ten minutes before you buy. Shops will usually let you do this, and it tells you more than any amount of standing in front of a mirror.

Keep the weight close to your back

Packing matters as much as the pack. The general rule is heavy items in the middle of the sack, close to your spine and roughly level with your shoulder blades. That keeps your centre of gravity near your own and stops the pack swinging you off balance on rough ground.

• Heavy kit, such as a tent, stove, food or water, goes in the centre, against your back.
• Light, bulky items like a sleeping bag go in the bottom compartment.
• Things you might need during the day, waterproofs, snacks, map, sit at the top or in the lid.
• Keep anything sharp or wet away from the fabric that touches your back.

Try to keep the total weight of a weekend pack under about a quarter of your body weight. Lighter is almost always more enjoyable, and a pack that carries well can handle a load that would defeat a poorly fitted one.

Features worth paying for

Once the fit is right, look at the details that make a difference over a weekend. A lid that can be removed or floated up gives you flexibility when the pack is stuffed or barely loaded. Side compression straps let you cinch down a part-full sack so it does not flop about. A decent hip belt with real pockets is genuinely useful for snacks and a compass.

For UK conditions, a pack that sheds rain reasonably and has a cover or a lined base is sensible. You do not need a fully waterproof sack, but a damp sleeping bag on night two is miserable. Ventilation panels on the back are nice in summer but add bulk; some walkers prefer a simpler, closer-fitting back panel that keeps the load stable.

Finally, check the harness against your waterproof jacket. Shoulder straps that sit badly over a bulky shell will chafe, and a hip belt that cannot be tightened through layers is worse than useless.

Test it properly before your trip

Buy your pack well before your weekend out, then load it and walk a few miles locally. Notice where it rubs, whether it shifts when you bend to cross a stile and how it feels after an hour. Small adjustments to the load-lifters or hip belt often solve niggles that seem serious at first. Learn to tune your own pack rather than fighting it, and a weekend in the hills becomes about the walking, not the carrying.