What Size Waterproof Bag Do You Need? 5L vs 15L Guide

Waterproof-bag sizes are quoted in litres, which doesn't mean much until you picture what you're carrying. Pick too small and you'll leave things behind; pick too big and you'll have a half-empty bag that's harder to roll. This guide translates litres into real gear.

Remember: you lose volume when you roll the top

The litre figure is the bag's full capacity. Once you roll the top down three or four times (which you must, for a waterproof seal), the space you can actually fill is a bit smaller. Size up slightly if you're packing something bulky — and never overfill to compensate, because an overfilled bag can't be sealed properly. See how to close a roll-top bag.

Size by size

The Rihla 5L

The Rihla 5L (20cm diameter x 25cm height) is the "everything I can't afford to get wet" bag: phone, wallet, keys, a small first-aid kit and a change of socks. It's small enough to sling across your body all day, and small enough to strap to a motorcycle rack or passenger seat.

The Rihla 15L

The Rihla 15L (21cm diameter x 37cm height) keeps a similar footprint but gets taller, so it holds a full change of clothes, shoes and food — a proper overnight load for one person. Pair it with a backpack for bulkier items like a tent.

Which one should you buy?

• Mostly the beach, the boat or the city? The 5L.
• Hiking or camping overnight? The 15L.
• A bit of everything? The 15L is the more forgiving choice — a half-full 15L is still easy to roll, while a 5L can't grow.
• Two people sharing a day out? One 15L, or a 5L each.

Still deciding? Our complete waterproof bag guide covers closures, seams and features, and you can see both bags side by side in the shop.