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Dry Bag Capacity Guide: 2L to 90L Explained

Why the printed litre number is not the volume you get

Nominal capacity is measured with the mouth fully open and the fabric relaxed, which is a repeatable laboratory condition and nothing like a packed bag. The usual method is to fill the body with water or calibrated beads up to the brim and print that figure. There is nothing dishonest about the method, but the number describes a container you will never actually use, because the closure has to happen above the waterline.

Three separate deductions sit between the printed figure and what you can really carry. The roll consumes body height, so the bag physically shortens. The closure needs slack, so you cannot fill to the brim. And real gear is irregular: a 1.7 L bottle behaves like 2.4 L of packing space once you count the dead corners around it. Add all three and a 20L bag behaves like a 14 to 16 L bag on a wet morning with cold hands.

How much capacity three folds really consume

Each fold of a roll-top removes a band of body height, and three folds remove about 9 cm on a mid-size bag. Multiply that by the cross-sectional area of the body and you have the loss in litres. A 20L bag with a 22 cm base has roughly 380 cm² of cross-section, so 9 cm of height costs about 3.4 L. The same 9 cm on a 2L bag with a 10 cm base costs only 0.7 L in absolute terms but 30 percent of the volume.

That is why small bags feel disproportionately cramped and large bags feel generous: the roll is a fixed tax measured in centimetres and a shrinking tax measured in percent. It also means the number of folds is a capacity decision, not only a waterproofing one. A fourth fold buys margin against a breaking wave and removes another 1.1 L from a 20L, which is a real cost when you are packing to the limit.

The 2L and 5L band: pocket kits and grab bags

Below 5L a dry bag is a pocket rather than a holdall. A 2L takes a phone, keys, a card wallet and a folded note with room to spare; a 5L swallows a compact first-aid pouch, a spare neck gaiter and a 500 ml bottle. Both sizes clip to a belt, a life jacket or a deck line, which is the whole point: they stay on your body during a swim, so the essentials never leave with the boat.

The failure mode in this band is overconfidence. Because a 2L feels small, people stuff it until the fold cannot close, and a roll-top closed under tension will weep rather than seal. Keep the fill to 1.4 L in a 2L and 3.8 L in a 5L, and treat anything bulkier as a job for the next size up. Two 5L bags beat one 10L whenever the contents need separating: wet swimwear in one, dry electronics in the other.

The 10L and 15L band: the day-trip workhorse

Between 10L and 15L sits the single most useful dry bag most people will ever own. A 10L takes a fleece, a light shell, a compact towel and a lunch box, which is about 7.9 L of real packing space and 2.4 kg on the shoulder. A 15L adds a camera body with one lens, or a second insulation layer for a trip that might run later than the forecast suggested.

The practical test is whether the bag still closes after you have packed for the worst case rather than the forecast. Pack for rain and a delayed return, roll it, and check that the buckle closes on the second notch rather than the last. If it closes on the last notch you are one extra layer away from a bag that cannot seal, and that is the moment to step up to a 20L rather than to force the closure.

The 20L and 30L band: camera kits and overnight loads

At 20L a dry bag becomes luggage. It holds a full day kit plus a camera: body, two lenses, spare batteries and a rain cover, which together pack to roughly 11 L and 3.6 kg. A usable volume of 16.4 L leaves the 30 percent headroom you want for a change of plan, and the bag still passes through a kayak day hatch or drops into a bicycle pannier without a fight.

At 30L you are in overnight territory: a summer sleeping bag at 8 L, a sleeping mat at 4 L, a stove and fuel at 3.2 L, plus clothing and food, all inside 25.2 L of usable space. Weight rather than volume becomes the constraint. A 30L filled with camping kit reaches 6 to 7 kg, which is comfortable on a padded harness for 400 m and punishing on a single shoulder strap over the same distance.

The 40L and 60L band: raft, canoe and basecamp

Raft and canoe trips change the maths because the bag never has to be carried far. A 40L swallows a two-person tent at 12 L, two sleeping bags at 16 L and a cooking kit, which is a 7 to 9 kg load moved perhaps 40 m from the vehicle to the water. Volume beats weight here, and the wide mouth of a 40L makes a shared load easy to sort at the end of the day.

At 60L, one bag becomes the shared kit for two or three people: group tent, food barrel, spare rope, dry suits. Filled to 52 L it weighs 10 to 14 kg, which means two grab handles are essential and a shoulder strap is decoration. Split group kit across two 30L bags instead if the portage crosses rocks, because a 14 kg soft bag is genuinely awkward to lift one-handed out of a boat.

The 90L band: expedition dumps and group kit

A 90L dry bag is not a bag you carry; it is a bag you stage. Expeditions use it as a gear dump strapped to a raft frame, as a shared clothing store on a multi-day sailing passage, or as the hold-all that rides in the vehicle until camp is set. At 79 L usable and 15 to 22 kg loaded, it needs two people, a cart or a frame to move any meaningful distance.

The risk at this size is not leakage but handling. A 90L bag dragged across gravel with 20 kg inside puts an enormous load on the base weld, and drag abrasion is the most common end-of-life story we hear in the largest sizes. Load it where it will be lifted, lift it with two people, and keep it off abrasive ground. If a trip genuinely needs 90 L of waterproof space, two 40L bags are easier on the bag and on your back.

Measuring capacity yourself with water or beads

1. Open the bag fully and stand it inside a tub so it cannot tip over.
2. Fill with water from a 2 L measuring jug until the level sits 20 mm below the fold line.
3. Record that figure as your maximum safe fill, not as the nominal size.
4. Roll and clip the top exactly as you would on a trip, then pour the contents back into the jug.
5. The second figure is your usable capacity; write both numbers on the body with a paint pen.
6. For printed or light-coloured fabric, repeat with 6 mm plastic beads and a marked 5 L bucket.

Water gives the most honest answer because it finds every corner, but it leaves you with a wet interior to dry. Plastic beads are faster, reusable and safe around printed graphics, and they understate capacity by 4 to 7 percent in bags with tapered corners. Either method takes about six minutes per bag and removes the guesswork when you are comparing a 15L from one range against a 20L from another; full method notes are in the capacity measurement guide.

Dimensional estimates are the third option and the weakest: multiplying base area by height with a tape measure is accurate to about 12 percent on a cylindrical body and worse on a tapered one. It is good enough to reject a listing that is clearly wrong and not good enough to choose between two sizes that are close. Whichever method you use, measure twice and record the numbers, because the same bag measured the same way in three years tells you how far the fabric has relaxed.

Capacity versus shape: when dimensions beat litres

Two 20L bags can behave completely differently. A tall, narrow 20L with an 18 cm base drops into a sea kayak hatch and sits beside a spare paddle; a squat 20L with a 28 cm base will not pass through the same opening even though it holds the same volume. Before buying on litres, measure the opening the bag has to pass through and add 2 cm of clearance for the buckle.

Shape also decides how the load sits in a boat. A low, wide bag spreads mass and keeps the centre of gravity down, which matters on a paddleboard where a tall bag catches wind at 40 km/h. A tall, narrow bag is better in a harness because it keeps the load close to your spine. Match the profile to the cavity first, then use litres to choose between two shapes that both fit.

Carry limits: matching size to distance and load

Every dry bag has a distance at which its carry system stops working. A single webbing handle is comfortable for about 150 m at 2 kg; beyond that it saws into the palm. A single shoulder strap moves a 10L for 500 m before the load starts to swing. Above 20L or 8 kg you want two padded straps, because a single strap on a heavy load twists the spine and is the usual reason for a sore shoulder after a portage.

Use the rule of 200 m: if a bag will be carried further than 200 m at more than 8 kg, buy the version with a harness rather than the version with a strap. The harness adds 180 to 260 g and roughly 12 percent to the price, and it is the cheapest comfort upgrade on the market. For anything above 60L, plan on a cart, a second person, or a boat that floats all the way to camp.

Building a three-size spread for one trip

Using one bag for everything is the most common packing mistake across the 2L to 90L range. Three sizes do a better job: one bag that stays on your body, one you can reach while moving, and one that stays closed until camp. On a two-day canoe trip that means a 2L on the belt, a 10L lashed within arm’s reach, and a 40L in the hull.

The spread buys redundancy as well as access. If a sharp branch breaches the 40L, you lose the tent but keep the phone, the first-aid kit and a dry layer. It also makes camp faster: one bag to the tent, one to the cooking area, one that never leaves your side. Colour-code the sizes so you can identify them by eye in poor light: a dark colourway for the hull bag, a bright one for the bag you need in a hurry.

Specifying a size ladder for a fleet or retail range

If you are buying for a rental fleet, a club or a retail shelf, the ladder matters more than any individual size. The eight-step ladder of 2, 5, 10, 20, 30, 40, 60 and 90 litres covers every realistic use case with no overlaps that cannibalise each other, and each step is at least 40 percent larger than the one below it, which is roughly the gap a buyer perceives as a genuine difference.

Standardise the closure across the ladder so users learn one system, and keep film thickness and hard points identical so a strap or a patch kit fits every size. Our production line has built waterproof bags since 2014 in an SGS-verified 4,950 m2 facility, with a 500-piece minimum per size, sampling in 6 to 10 working days and bulk in 35 to 50 days.

Verify any sample before you commit: test methods published by ISO and ASTM define how coated and laminated fabrics are measured, and a bag that quotes a standard is easier to compare than one that quotes an adjective. Then check the ladder against the full product line and against our roll-top dry bag range, where every size from 2L upward shares the same closure geometry.

Finally, read the small-size and large-size breakdowns before finalising a range: the 2L packing list, the 5L packing list, the 10L packing list and the 20L packing list each show real objects rather than theoretical litres, and the roll-top capacity loss guide explains exactly where the missing litres go.