First: get measured

Getting your back length measured is the surest way of finding the perfect pack. Many higher-capacity rucksacks come in Small, Medium and Large lengths, so knowing your back length is important. The measurement goes from the C7 vertebra (the pronounced knobble at the base of your neck) to a point on your spine halfway between the two wings of the iliac crest (the uppermost, outermost bones of your hips). A Medium is generally 18-22in, with Small and Large sitting either side of those figures. Need help? Osprey’s PackSizer app (pictured inset) does it for you using your phone’s camera.