Garden Cushion Storage: How Many Litres You Really Need

Garden cushion storage fails in one of two ways: the box is too small, so half the cushions end up in the shed or the hall, or the box is big enough but the cushions go in damp and come out in April smelling of mildew. Both are avoidable. This page works out how many litres your cushions actually take up, compares three real box sizes, and sets out how to pack them so they come out dry next spring.

Work out how many litres your cushions need

Storage boxes are sold by capacity in litres, but cushions are sold by size in centimetres, so most people guess. The sum is simple: multiply length by width by depth in centimetres and divide by 1,000 to get litres.

A dining chair seat pad of 40 x 40 x 5cm is 8 litres. Four of them are 32 litres, which fits in almost any box.
A deep lounge seat cushion of 60 x 60 x 15cm is 54 litres.
A matching back cushion of 60 x 45 x 15cm is about 40.5 litres.
A sun lounger pad of 190 x 55 x 5cm is about 52 litres, but its length is the real problem: it has to fold or roll to fit most boxes.

A typical rattan or timber lounge set with a three seat sofa and two armchairs has five seat cushions and five back cushions. Using the sizes above, that is 270 litres of seats plus about 202 litres of backs: roughly 473 litres in total. Measure your own cushions, because sizes vary a lot between sets, and add scatter cushions and throws on top.

Foam cushions compress a little when packed, but they spring back and push against the lid. Leave some headroom rather than filling a box to the brim; a lid forced shut on overfilled cushions will not seal against rain.

Three real box sizes compared

Keter’s resin boxes are among the most widely sold in the UK, and B&Q lists the specifications for several of them. As of October 2026:

Bar chart of Keter Comfy 270L, Darwin 380L and Darwin 570L capacities against a 473 litre lounge set — Box capacities against our worked example lounge set of about 473 litres | Chart by Best Garden Room

Keter Comfy 270L: 116.7cm long, 44.7cm deep and 57cm high, weather resistant resin, with wheels and a two year guarantee. Big enough for a dining set’s seat pads and a few scatter cushions, not a lounge set.
Keter Darwin 380L: 142.5cm wide and 65.3cm deep, about 55cm high, with a lockable lid on a hydraulic piston, a raised floor and ventilation. B&Q’s Darwin 380L listing says it seats two adults. Two year guarantee.
Keter Darwin 570L: the same 142.5cm width but 78.2cm high, lockable, two year guarantee. Of the three, it is the only one that would take the 473 litre example set with room to spare.

Check the internal dimensions as well as the litres. A 60cm square seat cushion will not lie flat in a box that is less than 60cm deep inside, and a box with a gas strut lid loses a little space where the strut is fixed.

Waterproof or weather resistant: read the wording

Retail listings use the words loosely. The same Darwin boxes are described on one page as having a “waterproof lockable lid” and elsewhere as “weather resistant”. In practice, a resin box with a hinged lid keeps rain off the contents but is not sealed: wind-driven rain can get past the lid edge, and water can sit around the base if the box stands on a lawn or in a low corner of the patio.

Three things make far more difference than the word on the label:

Where it stands. Put the box on paving or a level slab, ideally under the eaves of the house or a garden room overhang, never on grass.
A raised floor. Boxes with an elevated floor, as the Darwin range has, keep cushions off any water that gets in at the base.
Ventilation. A fully airtight box traps the moisture already in the cushions. Vents, or a lid that is not gasket sealed, let it out.

If you need something genuinely sealed, for example for electrical items, look for a product sold and tested for that job, and treat any cushion box as rain resistant, not watertight.

How to store garden cushions so they stay dry

Mildew in a cushion box almost always starts with cushions that went in damp. The steps that prevent it:

Dry them completely first. After the last use of the season, bring cushions indoors or into a dry shed for a day or two. Squeeze the corners: if the foam feels cool or damp inside, it is not ready.
Clean before storing. Brush off leaves, pollen and bird droppings. Follow the care label for washable covers and let them dry fully before refitting.
Do not seal them in plastic. Plastic bags trap moisture against the fabric. A breathable cotton bag or an old sheet keeps dust off and lets air move.
Stand them on edge. Cushions stood vertically, like books on a shelf, let air move between them and are easier to pull out than a flattened stack.
Air the box on dry days. Open the lid for an hour on a dry, breezy winter day, especially after a run of wet weather.
Check in midwinter. A quick look in January catches a leak or a damp corner before it spreads.

Cushions with a quick dry reticulated foam core and a solution dyed acrylic or olefin cover cope with damp far better than standard upholstery foam, but they still last longer stored dry.

Box, bench, shed or garden room?

A cushion box is not the only option, and the right one depends on how often you use the cushions.

Storage box or deck box. Best if cushions come in and out through the summer: they live next to the furniture and go away in a minute.
Storage bench. Smaller capacity, but it doubles as seating. Good for a dining set’s seat pads.
Shed. Fine if it is dry. Cushions on the floor of a damp, unlined shed often fare worse than in a good box; keep them on a shelf, off the floor, and see our garden shed storage ideas for shelving that frees up space.
Insulated garden room. The driest place in the garden if it is heated or ventilated. Worth it for expensive lounge sets.

For more on choosing, siting and building every kind of garden building, from sheds to garden rooms, see Best Garden Room.

Frequently asked questions

What size storage box do I need for garden cushions?

Multiply each cushion’s length, width and depth in centimetres, divide by 1,000 for litres, and add them up. A four chair dining set’s seat pads need about 32 litres; a five seat lounge set with back cushions can need around 470 litres or more.

Can I leave garden cushions in a storage box all winter?

Yes, if they go in completely dry, the box stands on paving rather than grass, and it has some ventilation. Air the box on dry days and check it in midwinter.

Are garden cushion boxes waterproof?

Most are rain resistant rather than sealed. Even boxes advertised with a waterproof lid can let in wind-driven rain at the edges, so siting and a raised floor matter more than the label.

Why do my garden cushions smell musty after storage?

They were stored damp, or moisture got in and could not escape. Dry them fully before storing, avoid plastic bags, and choose a box with ventilation.

Should I store garden cushions in plastic bags?

No. Plastic traps moisture against the fabric and encourages mildew. Use a breathable cotton bag or a sheet instead.

Where is the best place to store garden cushions in winter?

A dry indoor space, such as a heated garden room, spare room or loft, is best. A ventilated resin box on paving under cover is the next best option.