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5L vs 10L Dry Bag: Which to Buy

The short answer before the detail

If you are buying one bag and you cannot measure your load, buy the 10L. It absorbs the two mistakes people make most often: underestimating how much space soft goods occupy, and forgetting that a roll-top closure eats the top of the bag. A 10L packed to 8 litres still closes with three folds; a 5L packed to 5 litres does not close at all.

If you are buying two bags, buy one of each and give them different jobs. The 5L becomes the grab bag that lives where your hand reaches: a deck line, a harness strap, a bike handlebar. The 10L becomes the storage bag that lives in a hatch, a pannier or the bottom of a pack and is opened once or twice a day. Two different sizes used well beat two identical bags.

If you are buying for a child, a day hike or a gym kit, the 5L is usually right and the 10L is a blanket you will never fold. The honest test is to assemble the actual load on a table before you order: if it fits in a 5L with the top third empty, buy the 5L; if it fills a 5L to the brim, buy the 10L and thank yourself later.

Nominal versus usable volume: the roll-top tax

Every roll-top bag loses volume to its own closure, and the loss is not a fixed percentage. Three folds consume a band of fabric whose height depends on the fold radius and the mouth width, and the wider the mouth, the bigger the band. On a typical 5L bag with a 160 mm mouth, three folds take about 0.9 litres; on a 10L with a 210 mm mouth they take about 1.6 litres.

The percentage falls as bags get bigger because volume grows faster than mouth area, which is one more reason the 10L is the better default: it gives up a smaller share of its capacity to the same closure. The practical rule is to size for 85% of nominal volume and never plan a load that needs the top 15%.

Air makes the numbers worse in practice. Two soft items packed loosely can trap 1 to 2 litres of air that has to go somewhere, and if it cannot escape before the first fold it will push back against the seal from inside. Press the load down with a forearm, or use a purge valve if the bag has one, and the usable figure above becomes achievable rather than theoretical.

What actually fits in a 5L bag

A 5L bag is a one-job container. It holds a compact thermal top and a first-aid pouch, or a phone, keys, wallet and a snack, or a 1.2 kg lunch box, but not two of those groups at once. The failure mode is predictable: people buy a 5L, pack it to the brim with three soft items, fold once, clip, and then discover in the first wave that one fold is not a seal.

Read the last row carefully, because it is the real answer for a day out. The full list packs to about 10.4 litres, which means neither a 5L nor a 10L holds it. If that is your genuine load, you need a 15L or a two-bag split, and finding that out before you order is the entire point of measuring rather than guessing.

The case where the 5L is genuinely superior is access. A 5L is small enough to hang off a harness strap, stash in a kayak deck line or clip to a bike handlebar, and light enough that you forget it until you need it. Its job is the thing you want within arm's reach in the next 30 seconds, not the thing you need at lunch.

What actually fits in a 10L bag

A 10L bag is the first size that behaves like real storage. It swallows a spare thermal layer, a light shell, a compact towel and a first-aid pouch with room left for the closure, and it will take a small camera kit if you drop the towel. For a three-to-four hour paddle, a day hike or a full beach day with one other person, it is the correct default.

It is also the first size where weight starts to matter as a system. A 10L packed with 6 kg of gear is comfortable in a hatch and awkward on a shoulder strap, because a single strap on a soft bag concentrates the load on one point. If you intend to carry rather than stash, look at formats with two straps or a harness; the backpack versus duffel comparison covers that decision properly.

The 10L is the size most people keep the longest. It is large enough to be useful on a trip and small enough to live in a cupboard without dominating it, and it is the size that rental fleets and clubs standardise on because it fits almost any single-day load. If you only ever own one dry bag, this is the one to own.

Weight, dimensions and where each bag actually sits

Empty weight is where the two sizes come closest, which is why the 10L wins on value. A 0.3 mm TPU 5L weighs about 95 to 120 g and the 10L about 150 to 200 g; in 0.5 mm film those figures rise to roughly 140 to 170 g and 230 to 280 g. The 10L doubles the capacity for about 65% more weight, because film area grows more slowly than volume.

Packed footprint is a bigger differentiator than weight. A 5L is roughly 170 by 380 mm and slides into a kayak day hatch, a bike frame bag or the side pocket of a 35L rucksack. A 10L is roughly 220 by 470 mm, which fits a rear hatch or a pannier but not a frame bag and not most jacket pockets. Measure the opening you plan to push it through before you decide.

Film thickness is the variable people ignore and then regret. A 0.3 mm 5L is perfectly adequate as a deck bag that never touches sand; the same film on a 10L that gets stuffed into a hatch beside a pump and a paddle float will puncture within a season. Match thickness to abrasion, not to size: 0.3 mm for light duty, 0.5 mm for anything dragged or stuffed.

Cost per litre and cost per season

On sticker price the 5L looks like the thrifty choice, and on cost per usable litre it is not. At 15 USD for a 5L and 20 USD for a 10L, the 5L costs about 3.7 USD per usable litre and the 10L about 2.4 USD. You are paying a premium for the privilege of owning a bag that is too small for half the jobs you will ask of it.

Cost per season is the only metric where the 5L competes, and it does so only because the comparison assumes both bags survive the same number of years. In practice the 5L is more likely to be over-filled, which is the behaviour that kills closures, so its real service life is often shorter. Over-filling a bag is the fastest way to ruin a perfectly good seal.

For a fleet or a club the arithmetic flips again in favour of standardising. One size means one spare-part bin, one inspection routine and one training message for users. Most operations that start with a mix converge on a 10L plus a 5L within a season, which is exactly the two-bag split recommended above.

Activity match: which size for which trip

Activity is the cleanest way to settle the argument, because the load is defined by the activity rather than by preference. A trail run has one load, a day paddle has another, and neither cares much about what you feel like carrying. The table below assigns a size to eleven common activities with the reason in each case.

Two entries deserve a note. Bikepacking appears with both sizes because the volume is split by mounting position rather than packed together, and the two bags have different jobs: the 5L up front for snacks and a shell, the 10L at the seat for the sleeping layer. Travel appears with the 5L because a 10L of documents is a 10L of paper you will never read; see the carry-on packing guide for that specific case.

How size changes the closure and the seal

The closure geometry is identical in principle and different in practice. Both bags use three folds and a clip, but the 10L has a wider mouth, which means the fold line is longer and there is more opportunity for one corner to dip below the others. A dipped corner is the single most common cause of a slow leak, and it is more likely on a wide mouth than a narrow one.

The 5L is easier to close well. The mouth is narrow enough that a single hand can keep the fold line level across its width, and the shorter fold means less variation in fold radius. This is a real advantage on a moving deck or a windy beach, where a bag that is easy to close correctly is worth more than a bag that is theoretically better.

Both sizes should be closed the same way: expel the air, fold once along the reinforced line, fold twice more in the same direction, clip, and then sight down the fold line to confirm it runs straight across the mouth. The extra three seconds of visual check catches most closure errors. The physics behind the three-fold rule is set out in the roll-top closure guide.

Failure modes specific to each size

The 5L fails by over-filling. Its usable capacity is 4.1 litres and its temptation is 5, so it is routinely packed to the point where only one fold is possible, and one fold is not a seal. If you own a 5L and you have ever clipped it with a single fold, you have already met this failure and possibly blamed the bag.

The 10L fails by weight and by corner wear. Six kilos in a soft bag with a single strap puts real load on the top weld and on the D-ring attachment points, and a 10L dragged across a beach by one corner will wear through a 0.3 mm film in a season. Use 0.5 mm film for the 10L if it will be carried heavy or dragged, and check the corner welds monthly.

Both fail by grit, and the 5L fails faster because it is opened more often. Every opening is a chance for sand to land on the fold line, and a single grain is enough to create a capillary path that wicks water over an hour. Rinse the fold with fresh water before closing on any beach, and run a thumb along the line to feel for grit.

When a third size beats both

There is a band of loads where neither size is right, and recognising it saves money. Loads between 8.5 and 12 litres need a 15L, and loads under 2 litres are better served by a 2L that can be clipped somewhere useful. Buying a 5L and a 10L and then forcing every job into one of them is how people end up with four bags when three would do.

The 2L deserves particular mention as a companion rather than a competitor. A phone, keys, a card and a small camera fit in a 2L, and the 2L can be dropped inside either bag as a second independent seal for electronics. Two independent seals are worth more than one thick one, because a failed closure is far more likely than a failed film.

If you are assembling a range rather than a personal kit, the natural ladder is 2L, 5L, 10L, 20L and 40L. Each step roughly doubles the previous one, which keeps the decision simple for a buyer and avoids the paralysis of seven near-identical sizes. The full ladder is mapped in the capacity guide from 2L to 90L.

Ratings, standards and what to check on the spec sheet

Size does not change the rating, but it changes how the rating is achieved and how easily it is lost. A 5L and a 10L from the same range should carry the same ingress grade, usually IPX7 for a welded roll-top, meaning 30 minutes at one metre under IEC 60529. The IEC defines those grades, and a spec sheet that names the standard is worth more than one that simply says waterproof.

Check three lines specifically: the film thickness in millimetres, the ingress grade with its standard, and the stated usable or packed volume if the brand publishes one. Also check the seam type, which should be welded rather than taped or sewn, and confirm that any load-bearing D-ring is welded rather than stitched to the body. Those five lines predict field performance better than any photograph.

Weight and bulk claims are worth a sanity check against the ASTM textile and fabric test language used in most spec sheets, because a published dimension is only comparable if it was measured the same way. Two brands quoting 170 by 380 mm for a 5L may be measuring flat, rolled or packed, and the difference is not trivial when you are squeezing a bag into a frame bag.

Decision rule and buying checklist

1. Assemble the real load on a table and estimate its volume in litres.
2. Add 15% for the closure; if the result is under 3.5 L buy the 5L, under 7 L buy the 10L.
3. Measure the opening the bag must pass through: frame bag, hatch, pannier or pocket.
4. Choose 0.3 mm film for light duty and 0.5 mm for dragged, stuffed or fleet use.
5. Confirm welded seams, welded D-rings and an ingress grade tied to IEC 60529.
6. Check the mouth width: narrower mouths seal more easily on a moving deck.
7. If two sizes remain plausible, buy both and assign each a different position.
8. Test the bag in a bath the day it arrives, before the trip that matters.

The final rule is the one that survives every edge case: size for the load plus 15%, never for the number on the bag, and never for the price. A bag that is one size too small will be over-filled, and over-filling is the failure mode that destroys closures. A bag that is one size too large is a minor annoyance you will barely notice.

Related reading if you want the detail behind the numbers: the 5L packing list and the 10L packing list both give item-by-item volumes, and the capacity loss notes explain the roll-top tax in more depth. Our roll-top range covers both sizes in 0.3 mm and 0.5 mm TPU, and the full product line shows where they sit in the ladder.

Production has run since 2014 in an SGS-verified 4,950 m2 facility with 137 staff across seven lines, and both sizes are built on the same welding platform with AQL 2.5 inspection on every run. Sampling takes 6 to 10 working days and bulk 35 to 50 days, FOB Xiamen, with a 500-piece minimum per size and colourway. We document the full process from sampling to bulk. If you are choosing between two sizes for a range rather than for yourself, see the broader sizing comparison.