Hiking Pack Volume Calculator: What Size Backpack Fits Your Gear List

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What size backpack do you actually need?

Backpack sizes are sold in litres, but most people buy by guesswork. Too small, and gear hangs off the outside or gets left behind. Too big, and you carry extra fabric and a pack that never sits right. The right size follows from your gear list, and this calculator adds that list up for you.

Tick the gear you carry, add any extra volume for items not listed, and the tool totals your gear volume and recommends a pack size with a little spare room. The recommendation leaves about 15 percent free, because a pack stuffed to the last litre is hard to close, hard to unpack, and uncomfortable to carry.

How to use the calculator

Go through the checklist and tick everything you plan to carry: tent, sleeping bag, pad, stove, cook set, clothes, food bag, water, first aid kit, and rain jacket. If you carry something not listed, like a camera or a book, estimate its size and add it as extra litres. A camera bag is roughly 2 litres, a paperback about 1 litre.

The result shows two numbers. The first is your gear volume, the plain total of everything you ticked. The second is the recommended pack size, rounded up to the nearest 5 litres, which is how packs are usually sold. Buy near that number, not far above it.

How the volumes work

The volumes are typical packed sizes for standard gear. A two-person tent packs to about 6 litres, a sleeping bag to about 8, and spare clothes to about 8. These are honest averages, not maker claims. Ultralight gear packs smaller, and bulky budget gear packs larger, so adjust with the extra litres box if your gear is unusual.

The 15 percent margin covers the awkward reality of packing: gear never fills a pack perfectly, and you always need room for a snack, a map, or a layer you take off mid-walk. A pack that fits exactly on paper will feel too small on the trail.

A worked example

A weekend hiker ticks a two-person tent, sleeping bag, pad, stove, cook set, clothes, food bag, and 2 litres of water. That totals 39 litres. With the margin, the recommendation is 45 litres. A 40-litre pack would be a tight squeeze, while a 65-litre pack would be mostly empty and floppy. The 45-litre recommendation is the sweet spot for this kit.

Planning tips

Pack heavy items close to your back and near the middle of the pack height. That keeps the load stable and saves your shoulders. Put things you need during the day, like a rain jacket, snacks, and a map, at the top or in side pockets. Use dry bags inside the pack rather than trusting a rain cover alone, because rain covers blow off and leak at the seams.

If you are between sizes, choose the smaller pack and trim gear before choosing the bigger pack and filling it. Packs expand to fill the space you give them, and a half-empty big pack carries worse than a full small one. Weigh the full pack before a trip: for most walkers, a comfortable load is under a fifth of body weight.

Frequently asked questions

Does food count in the volume? Yes, and it shrinks as you eat it. Size the pack for the first day, when food volume is largest, not the last day. The food bag figure here covers a day or two of food for one person.

What about winter gear? Winter adds bulk fast: a warmer bag, more clothes, and maybe traction gear. Add those as extra litres. A summer 45-litre pack often becomes a 60-litre pack in winter for the same person.