How to get bed linen sizes right for your mattress

Measure the mattress, not the bed frame

Size names on packaging are a starting point, not a promise. Two mattresses sold under the same name can differ by a few centimetres, and that small gap decides whether a sheet lies flat or wrinkles by morning.

Length and width

Take the bedding off and measure the bare mattress. A rigid tape gives a truer reading than a soft dressmaker's tape, which can stretch with age. Measure across the widest point from side to side, then from the head end to the foot. Note both figures down rather than relying on memory when you shop.

Depth, the figure most people forget

Depth causes more badly fitting sheets than length or width. Deep mattresses with pillow tops, and thinner ones finished with a topper, can be far taller than older designs. Measure the side of the mattress from the lower seam to the upper one, and if a topper or quilted protector stays on the bed, measure with it in place.

A fitted sheet needs a pocket a little deeper than that figure, so the elastic edge can curl under the mattress and hold. Many packs state the maximum depth the sheet will fit; check that number against your own.

Size names change with the country

Labels use familiar words such as single, double, king and super king in the UK, or twin, full, queen and king in North America. The words travel; the measurements do not. Continental European mattresses are often a little longer than British ones, and North American sizes follow a different set of widths altogether. A sheet labelled king in one market will not necessarily fit a king bed bought in another.

The safest habit is to ignore the name until you have read the measurements printed on the packaging, and to compare them with your own. When a bed has been bought abroad, or a mattress replaced with one from a different maker, this check matters even more. Any size chart you find is best read as typical rather than fixed.

Fitted and flat sheets

Fitted sheets suit people who want a quick, smooth bed. Flat sheets give more freedom with tucking and double as a light cover in warm weather. Each has its own fit points.

Corners and elastic

A fitted sheet has boxed corners cut to the shape of the mattress. A pocket that is too shallow pulls off at the corners as soon as someone turns over; one that is too deep leaves loose fabric gathering under the sleeper.

Elastic around the whole edge, rather than only at the corners, grips more evenly and is more forgiving of a slightly deeper mattress. Woven cotton and linen have no stretch of their own, so the cut of the pocket does most of the work.

How much a flat sheet should overhang

A flat sheet needs enough fabric to tuck under both sides and the foot of the mattress, with spare length at the top to fold back over the duvet or blanket. A simple way to judge it is to add twice the mattress depth to the width, then allow extra for a generous tuck. Do the same for the length, adding a fold at the top. A sheet that barely reaches the underside of the mattress will pull loose overnight.

Duvet covers and pillowcases

Covers protect what is inside them, and both duvets and pillows keep their shape better when the cover is the right size.

Matching the cover to the duvet

Buy the cover by the duvet's size name and check that the measurements agree. A cover that is too tight compresses the filling into ridges and strains the seams; a loose one lets the duvet bunch at the foot and leaves flat, empty corners at the top. Corner ties or tabs inside the cover help keep the duvet in place, especially with lighter fillings.

Natural fibres can shrink a little in early washes, so it is worth following the care label from the start. Avoid a very hot tumble dryer for the first few cycles, and the cover is far more likely to keep its intended size.

Pillowcase shapes

Pillows come in more shapes than beds do. Rectangular pillows are the everyday sleeping format in the UK, with a longer version made for wide beds so that two pillows can span the mattress without a gap between them. Square pillows, often called continental or European, are common elsewhere in Europe and are frequently used upright against the headboard for reading. Pillow sizes vary between makers too, so measure the pillow itself before buying cases.

The way a pillowcase closes also affects how it looks on the bed:

• A housewife closure has an inner flap at one end that holds the pillow in, with a clean, plain edge on show.
• An Oxford case has a flat border of fabric around all four sides, which frames the pillow and suits a more tailored bed.
• Button or zip closures hold firmer fillings securely and are common on square cases.

A case should be a touch larger than the pillow so the filling is not squeezed flat, but not so loose that the pillow slides around. With the mattress depth, the size name and the pillow measured, most fit problems disappear before the linen reaches the bed.

Frequently asked questions

How much extra depth is needed for a fitted sheet pocket?

Choose a pocket a little deeper than the mattress so the elastic can reach underneath. If you use a topper or a thick protector, measure the depth with it in place.

Why do bed sizes with the same name differ?

Size names such as double, king or queen follow national and maker conventions. A king in one country can be a different width or length from a king in another, so the measurements on the label matter more than the name.

Should a duvet cover be the same size as the duvet?

It should match the duvet's size name and measurements as closely as possible. A cover that is too small squashes the filling; one that is too large lets the duvet slip and leaves empty corners.

Do linen and cotton sheets shrink?

Natural fibres can shrink slightly in the first few washes, linen and loosely woven cotton more than prewashed fabrics. Following the care label and avoiding very hot tumble drying keeps shrinkage to a minimum.