What Size Dry Bag Do I Need? The Complete Guide to Choosing the Right Waterproof Bag
28 March 2026
Not sure which dry bag size is right for you? This complete guide breaks down every size from 5 to 55 litres, with real-world examples of what fits inside each one — so you can choose the perfect bag for your next adventure.
Wondering what size dry bag you need? Choosing the right dry bag size is one of those things that seems simple until you’re standing in front of six different options wondering whether your sleeping bag will fit in a 10-litre or if you actually need a 30. Get it wrong and you’re either cramming gear in with a crowbar or carrying a half-empty bag that flaps around on your back.
We’ve been making waterproof dry bags for over seven years and our bags are trusted by International Search and Rescue (ISAR) teams worldwide. So we know a thing or two about matching the right bag to the right job. Here’s our no-nonsense guide to choosing the perfect size. Whether you’re comparing dry bag sizes for a weekend trip or looking for the best dry bag size for a specific activity, we’ll help you find the right waterproof bag sizes for your needs.
Dry Bag Size Guide: Quick Reference
| Size | Best For | Price |
|---|---|---|
| 5 Litre | Phone, keys, wallet, small valuables | £13.99 |
| 10 Litre | Towel + change of clothes (child) or day essentials | £15.99 |
| 20 Litre | Full change of clothes (adult), day trips | £19.99 |
| 30 Litre | Overnight trips, larger day packs | £24.99 |
| 35 Litre | Multi-day expeditions, DofE, hiking | £38.99 |
| 55 Litre | Extended expeditions, full camping kit | £45.99 |
5 Litre Dry Bag — The Essentials Pouch
Whether you need a dry bag for backpacking or water sports, the 5L is your grab-and-go bag for small valuables. Think of it as a waterproof safe for the things you absolutely cannot afford to get wet.
What fits inside a 5L dry bag:
- Phone, keys, and wallet
- Car keys and a small snack
- A compact camera
- Basic first aid supplies
Best for: Kayakers who need cockpit essentials within reach. Swimmers keeping valuables safe on the bank. Or as an inner bag inside a larger dry bag to separate wet and dry kit — a trick used by experienced DofE expedition leaders.
10 Litre Dry Bag — The Beach & Day Trip Bag
Our original and still one of our most popular sizes. The 10L is the perfect companion for a day at the beach, a kayaking session, or any activity where you need to keep a small amount of gear safe and dry.
What fits inside a 10L dry bag:
- A beach towel and a child’s change of clothes
- A 4-season sleeping bag (compressed)
- A tablet, book, and snacks
- Shoes, socks, and a spare t-shirt
Dimensions: 55 cm x 30 cm (21.75″ x 11.75″) when laid flat.
Best for: Beach days, short kayak trips, river crossings, and keeping essentials dry during water sports.
20 Litre Dry Bag Backpack — The Day Pack
Step up to the 20L and you’ve got a proper day pack. This is our go-to recommendation for adults who need a full change of clothes kept dry, or anyone heading out for a day on the water with more than just the basics.
What fits inside a 20L dry bag:
- A full adult change of clothes including shoes
- A towel, toiletries, and a spare layer
- Lunch, water bottle, and snacks for a day trip
- Camera equipment and accessories
Dimensions: 70 cm x 36 cm (27.25″ x 14.25″) when laid flat.
Best for: Day trips on the water, canoeing, paddle boarding, cycling in the rain, and commuting.
Shop the 20L Dry Bag Backpack — £19.99
30 Litre Dry Bag Backpack — The Versatile All-Rounder
The 30L sits in that sweet spot between a day pack and an expedition bag. It’s big enough for an overnight trip but still compact enough for everyday use.
What fits inside a 30L dry bag:
- Everything in the 20L plus a sleeping bag
- Overnight kit for a one-night wild camp
- A full day’s food, water, and spare layers for hill walking
- Wetsuit, towel, and change of clothes for surf trips
Best for: Overnight adventures, longer kayak trips, surf sessions, and anyone who needs a bit more space without going full expedition size.
Shop the 30L Dry Bag Backpack — £24.99
35 Litre Waterproof Backpack — The Expedition Favourite
Our best-selling backpack and the bag of choice for Duke of Edinburgh expeditions. The 35L has comfortable padded shoulder straps, a roll-top closure, and enough room for a multi-day trek without encouraging overpacking.
What fits inside a 35L dry bag backpack:
- Sleeping bag, sleeping mat, and spare clothes
- Food and cooking kit for 2–3 days
- Waterproofs, warm layers, and a first aid kit
- Map, compass, and navigation equipment
Best for: DofE Bronze, Silver, and Gold expeditions. Hiking and wild camping. Multi-day kayak trips. Anyone who needs a serious waterproof backpack that eliminates the need for a rain cover.
Shop the 35L Waterproof Backpack — £38.99
55 Litre Waterproof Backpack — The Full Expedition Pack
Our biggest bag for those who need to carry everything. The 55L is built for extended expeditions, Gold DofE trips, and anyone carrying group kit. Same bulletproof waterproof construction, just with serious capacity.
What fits inside a 55L dry bag backpack:
- Everything in the 35L plus tent poles, extra food, and group cooking equipment
- Full camping setup for 3–5 day expeditions
- Bulky winter layers, extra fuel, and emergency supplies
Best for: Gold DofE expeditions, extended wild camping trips, multi-day kayak touring, and situations where you’re carrying shared group kit.
Shop the 55L Waterproof Backpack — £45.99
Still Not Sure? Here’s How to Decide
Still not sure how to choose a dry bag? Ask yourself three questions:
- What am I putting in it? — Just valuables? Go 5L. A full change of clothes? 20L. Multi-day expedition kit? 35L or 55L.
- How long am I out for? — Day trip = 10–20L. Overnight = 30L. Multi-day = 35–55L.
- Do I need to carry it on my back? — Our 20L and above come with backpack straps. The 35L and 55L have padded, adjustable straps designed for all-day comfort.
And remember — every Ultra Dry bag is 100% waterproof, not just water-resistant. No rain covers, no spray-on treatments, no crossed fingers. Our bags are trusted by International Search and Rescue (ISAR) teams, so whatever size you choose, your kit stays dry. Every bag also comes with our 5-Year Guarantee.
Buying for a Group?
If you’re equipping a school, DofE group, club, or organisation, we offer a B2B price list with up to 30% discount on bulk orders of six cartons or more. Contact mark@ultradrybags.co.uk for pricing.