Answer

By Country Walking magazine

Rucksack sizing is a mysterious art, with packs covered in all kinds of numbers. If a rucksack sports a sizing such as 35+8, it means that the main compartment has a 35-litre capacity, but there are roomy side pockets and/or a floating lid (a lid attached to the pack with extendable tapes rather than sewn on, so it lifts as you stuff your pack fuller and fuller), which can increase the capacity by another 8 litres. So packed full, it’ll have a capacity of 43 litres.

One thing to remember though - packs labelled the same size do seem to vary from one manufacturer to another. So it’s worth taking all your walking kit down to the shop when you buy, and spend an afternoon packing and unpacking rucksacks to find the perfect one for you.