Guide · Storage & home · 4 models
How to measure your space before buying storage boxes: litres describe volume, not shape
A 50-litre box can be lower than a 35-litre one, and an under-bed box that is one centimetre too tall does not go under the bed at all. Measure the gap first — height, then depth, then width — and buy by external dimensions. Worked examples with the makers' own measurements for boxes that fit under beds, on shelves and in fridges.
Height first, then depth, then width, then litres
Storage is sold by litres because litres are easy to print, and litres are the last thing that matters. A box fails on height — it does not go under the bed — long before it fails on capacity. So measure in this order: the height of the gap, the depth of the space (how far in it goes), the width, and only then ask how many litres a box of those outer dimensions can hold. Every figure below is the maker’s own external measurement, which is the one to compare with a tape measure.
Under the bed
Measure from the floor to the lowest part of the bed frame — the bottom of the slats or the rail, not the mattress — at several points, because frames sag and floors are not level. Subtract 2 to 3 cm for sliding. That number decides the category.
18 cm — the standard under-bed height
Wham Crystal 32 L under-bed box, set of 5
- Length
- 60 cm
- Width
- 40 cm
- Height
- 18 cm
- Capacity per box
- 32 L
- Weight per box
- 1.12 kg
- Moves on
- Integral sliders (no wheels)
Check price on Amazon.co.uk
At 18 cm high, 60 cm long and 40 cm wide, Wham’s Crystal 32 L is the standard under-bed proportion: a gap of 20 to 21 cm is enough, and the integral sliders mean it needs no extra height for wheels. The 32 litres is what that shape yields; buying it for the litres would be backwards.
Strengths
- 18 cm high — the lowest rigid box here
- Integral sliders, so a full box pulls out without wheels
- Made in Britain by What More UK
Limitations
- The listing is unclear whether you get five boxes or ten
- Sliders, not wheels — a full box drags on carpet
- Clear lid shows the clutter as well as the contents
Good for
- a slatted or metal bed with 20 cm or more of clearance
- seasonal clothes and shoes split across equal boxes
Look elsewhere if
- a bed with under 20 cm of clearance
- anyone who wants one big box rather than five small ones
23 cm — more litres, still low
Really Useful Box 50 L
- Length
- 71 cm
- Width
- 44 cm
- Height
- 23 cm
- Internal space
- 60.5 × 37 × 20 cm
- Capacity per box
- 50 L
- Weight per box
- 2.62 kg
Check price on Amazon.co.uk
Really Useful’s 50 L is the counter-example that makes the point: more than half again the volume of the Wham, and only 5 cm taller at 23 cm, because it is 71 cm long and 44 cm wide. It wants a 25 to 26 cm gap and a bed at least 75 cm wide to disappear under. Compare that with a tall 35-litre box of the same brand’s stacking range, which is over 30 cm high and would not go under a bed at all — same brand, fewer litres, wrong shape.
Strengths
- 50 litres in a single box, 23 cm high
- The handles lock the lid — safe to carry full
- Really Useful publishes the internal space: 60.5 × 37 × 20 cm
Limitations
- 23 cm high — needs the most clearance of the six
- No wheels or sliders, and 2.6 kg before you fill it
- Sold singly
Good for
- a bed with 25 cm or more of clearance
- bulky items: bedding, winter coats, boxed things
Look elsewhere if
- low frames
- sliding in and out every week
15 cm — fabric for the lowest gap
SONGMICS under-bed storage bags, set of 2 (RUB002G01)
- Length
- 82 cm†
- Width
- 40 cm†
- Height
- 15 cm†
- Bags in the pack
- 2†
- Moves on
- Carried by handles; folds flat when empty†
- Lid
- Zipped transparent lid†
Check price on Amazon.co.uk
Below 18 cm the rigid boxes run out and fabric takes over. SONGMICS’ fabric drawers are 15 cm high and 82 cm long; a 17 cm gap is enough. The trade is rigidity — a fabric drawer full of jumpers holds its shape, one half full does not — and the length: 82 cm needs a bed of at least 85 cm to hide behind.
Strengths
- 15 cm high — fits where rigid boxes do not
- Transparent lid and a Velcro divider to split seasons
- Folds flat when empty
Limitations
- Cardboard-stiffened fabric, not a rigid box
- 82 cm long — measure the depth of the bed first
- Every dimension comes from the listing, not from SONGMICS
Good for
- low beds and sofas
- seasonal clothes and blankets
Look elsewhere if
- damp rooms — the stiffening is cardboard
- heavy or sharp-cornered items
no fixed height at all
Spacesaver Jumbo vacuum storage bags, 5-pack
- Bag length
- 102 cm†
- Bag width
- 76 cm†
- Bags in the pack
- 5†
- Pump
- Hand pump included†
- Seal
- Double-zip seal with a one-way valve†
- Material
- Polypropylene film†
Check price on Amazon.co.uk
And below 15 cm, or for anything soft you touch twice a year, vacuum bags have no fixed height at all: a duvet compresses to whatever the pump leaves. They are wrong for anything used weekly and wrong for feather fillings stored compressed for months, but for the lowest gap they are the only answer.
Strengths
- Flattens duvets and pillows that no box will take
- Hand pump included — no vacuum cleaner needed
- Reusable double-zip seal
Limitations
- Compressed thickness depends on the contents — no fixed height to plan around
- Down and feather bedding does not like long compression; check the care label
- Bags, not boxes: no protection from knocks
Good for
- spare duvets and winter bedding
- the shallowest gaps
Look elsewhere if
- things you use every week
- delicate or structured items
On a shelf
Two measurements: the shelf depth, minus the door, and the height to the shelf above, minus the lid. A 35 cm-deep wardrobe shelf with a hinged door takes a box up to about 32 cm deep. A box with a lift-off lid on a shelf with 25 cm above it needs the lid to lift off within that 25 cm — a 23 cm box with a 3 cm lid clearance is marginal; a clip-lid box whose lid hinges or comes off sideways is not. This is why under-bed boxes make bad shelf boxes: their proportions are long and low, and the shelf is short and high.
In a fridge and cupboard
Food containers are the same problem at a smaller scale. A fridge shelf might have 12 cm between shelves; a 2-litre box that is 8 cm tall fits and a 2-litre round tub that is 14 cm tall does not. Makers of the better container ranges publish per-box dimensions — Sistema gives each KLIP IT box’s length, width and height in millimetres — and the rule is the same: match the height to the shelf, then the footprint to the shelf depth, then choose the volume that shape gives you.
Measuring well
- Use a tape, not a guess, and measure the gap at its smallest point.
- Under beds, measure to the frame or slats at both ends and the middle.
- Subtract 2–3 cm for sliding, more for wheeled boxes (add the wheel height).
- Note all three numbers — height, depth, width — and compare with the maker’s external dimensions, not the litres.
- If a listing gives litres and no dimensions, treat it as unknown.
Sources
Facts checked 24 September 2026
- What More UK (Wham) — Crystal 32L U/bed Box & Lid, product code 10860 — Manufacturer documentation, checked 23 September 2026
- Amazon.co.uk listing (Wham) — Retailer listing, checked 23 September 2026
- Really Useful Products — 50 litre Really Useful Box — Manufacturer documentation, checked 23 September 2026
- Amazon.co.uk listing (Really Useful Box) — Retailer listing, checked 23 September 2026
- Amazon.co.uk listing (SONGMICS) — Retailer listing, checked 23 September 2026
- Amazon.co.uk listing (Spacesaver) — Retailer listing, checked 23 September 2026
How much clearance do I need under the bed?
Measure from the floor to the lowest part of the frame or slats, not to the mattress, and subtract 2 to 3 cm so the box slides rather than scrapes. An 18 cm box (Wham Crystal 32 L) wants a 20 to 21 cm gap; a 23 cm box (Really Useful 50 L) wants 25 to 26; a 15 cm fabric drawer (SONGMICS) fits a 17 cm gap. Wheeled boxes add the wheel height on top.
What size is a 35 litre box?
It depends entirely on the shape. Litres are volume; a tall square 35 L box and a long shallow 35 L box are different objects for different gaps. The only way to know whether a box fits is the maker's external dimensions — length, width and height — which every serious storage brand publishes. If a listing gives only litres, look elsewhere.
Do boxes fit under a divan bed?
Only if the divan sits on legs or a raised plinth with a real gap. A divan on castors with a solid base, or one with drawers, leaves nothing usable; the storage is the drawers. Measure the gap at the lowest point of the base — divans often sag toward the middle.
How deep should a shelf box be?
Measure the shelf depth and subtract enough to close the door: a 35 cm wardrobe shelf takes a box up to about 32 cm deep. Then check the height against the shelf above, minus the lid's lift-off height if the lid comes straight up rather than hinging — a lidded box on a shelf needs room to open.
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