What Size Dry Bag Do You Need? A Practical Packing Guide
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A dry bag's litre rating is a starting point, not a promise that your particular kit will fit comfortably. A folded jacket, a lunch box and a camera case use space differently. Start with the contents, then choose the capacity and construction.
Make a list before choosing a size
Separate your equipment into groups: spare clothing, food, sleeping equipment and small essentials. Write down what must remain dry and what you need to reach during the day. This prevents one large bag from becoming the answer to several different problems.
Sea to Summit's size guidance gives broad examples: smaller bags for compact essentials, mid-size bags for clothing or food, and larger bags for bulkier equipment. Treat these as examples rather than a packing guarantee. A thick winter layer and a thin summer layer do not occupy the same space.
Check the packed shape as well as the litres
Measure rigid objects and compare them with the bag's published dimensions and opening. A container can have an awkward shape even when its nominal volume looks modest. Check whether the dimensions describe the open bag or the bag with its closure rolled.
Leave enough space to close the bag exactly as its manufacturer instructs. If packing your kit requires stretching the opening or reducing the required closure rolls, choose a different capacity or split the load.
One bag or several?
| Approach | Useful when | Trade-off to consider |
|---|---|---|
| One larger bag | You want a simple packing arrangement | Accessing one item can mean opening the whole load |
| Several smaller bags | You want separate groups of equipment | More closures and bags to manage |
This is an organisational choice, not a claim that either arrangement is automatically more waterproof. Each bag still needs a suitable construction, correct closure and appropriate use.
Do a dry packing rehearsal
- Gather the exact items you intend to carry.
- Pack them without forcing rigid corners against the fabric.
- Complete the manufacturer's closure procedure.
- Check that the bag fits where you intend to carry it.
- Take out one frequently used item and check whether the arrangement remains practical.
Do this at home, with dry contents. Do not use valuable electronics to experiment with waterproof performance. Sea to Summit advises that roll-top dry bags should not be submerged.
Capacity is only one part of the decision
Once the size is right, consider carrying weight, attachment points and intended use. Our Lightweight vs Big River 13L comparison examines two bags with the same stated capacity but different constructions. It helps answer a different question: which features fit your use?
Sources and method
Manufacturer information checked on 11 October 2026. Product instructions take priority. This guide combines documented information with e-grin's practical decision framework; it does not report hands-on testing.
Read Our Method for how we evaluate information and limitations.