What Size Dry Bag Do I Need? 5L to 55L Compared
3 August 2026
For most people, a 10–20 litre dry bag is the right size: big enough for a towel, a change of clothes, your phone and lunch, but not so big it becomes a sail on your paddleboard. Go smaller (5L) if you only need valuables kept dry, and bigger (35–55L) if you’re carrying kit for a full day or a multi-day trip.
Here’s how the sizes compare, based on what our customers actually use them for.
What do the litre sizes actually mean?
A dry bag’s litre rating is its total internal volume. As a rule of thumb, 1 litre holds about one rolled-up t-shirt. Remember you lose a little capacity to the roll-top closure — you need at least three folds at the top for a proper seal — so if you’re between sizes, size up.
Dry bag size comparison
| Size | What fits | Best for |
|---|---|---|
| 5L | Phone, keys, wallet, snacks, a light layer | Kayak day trips, keeping valuables dry on any boat |
| 10L | Towel, change of clothes, phone, snacks | Sea swimming, SUP, gym-and-swim days |
| 20L | Full change of clothes, towel, lunch, first-aid kit | Day paddles, canoe camping day kit, beach days |
| 30–35L | Everything for a full day out, or one person’s weekend kit | Duke of Edinburgh expeditions, winter swimming (more warm layers), kayak touring |
| 55L | Multi-day expedition kit or two people’s day kit | Expeditions, sailing weekends, family beach days |
What size dry bag do I need for kayaking?
A 5L or 10L bag clipped inside the cockpit covers valuables and a dry layer. If you’re touring or camping from the boat, a 30L or 35L backpack-style bag stows well in a hatch and carries comfortably on the portage.
What size dry bag do I need for paddleboarding?
10–20L strapped to the front bungees is the sweet spot — a full change of clothes and your valuables, without catching the wind. Our 20L dry bag backpack also has shoulder straps for the walk to the water.
What size dry bag do I need for sea swimming?
Two answers: a 10–20L bag on the beach for your towel and clothes, or a 28L tow float dry bag that comes swimming with you — it keeps you visible to boats and carries your kit at the same time, so nothing is left unattended on the shore.
Still not sure?
Our 10, 20 & 30 litre rucksack 2-pack is the easy answer — a small bag for valuables and a bigger one for kit. Every Ultra Dry bag is made from 7.5mm pure-grade polymer, comes with a waterproof phone case in the box, ships UK-wide, and is covered by our 5-year guarantee.