Quick answer: Strip the bed, then measure the width across the middle from side to side, the length down the centre from head to foot, and the depth from the base to the top at one edge. Record it as width × length × depth in centimetres, such as 135 × 190 × 25 cm for a UK double.
Measuring a mattress takes two minutes, yet it is the step most often skipped when people buy a replacement, a topper or a set of fitted sheets. This guide, part of our home measuring guides, shows where to put the tape, how to read the result against the standard sizes in our UK bed sizes chart, and what to do when your numbers do not match the label.
What do you need to measure a mattress?
A tape measure at least 2.5 m long, a straight edge and ideally a second person. The straight edge can be a spirit level, a long ruler or even a hardback book; it lets you measure depth accurately where the edge of the mattress is rounded.
- A retractable steel tape or a fabric tailor’s tape (see how to read a tape measure for the markings)
- A straight edge: a spirit level, long ruler or anything flat and rigid about 30 cm or longer
- A notepad or phone to write the three figures down
- A helper to hold the far end of the tape for the length
How do you measure a mattress step by step?
Take three measurements across the middle of the mattress with the bedding removed, then round each to the nearest centimetre. Follow the order below so you do not have to move the mattress twice.
- Strip the bed. Remove the sheets, any protector and any topper. Even a thin protector adds bulk at the corners.
- Measure the width. Run the tape across the top surface at the halfway point, from one side edge to the other. Check it again near the head and foot; if the three readings differ by more than a centimetre or two, use the middle figure.
- Measure the length. With a helper holding the end, run the tape down the centre from the head edge to the foot edge. Keep the tape flat on the surface rather than letting it sag over the ends.
- Measure the depth. Lay your straight edge across the top so it sticks out past one side. Measure straight down from its underside to the bottom of the mattress where it meets the base.
- Write it down in the standard order. Width × length × depth, in centimetres. Retailers in the UK list sizes this way.
- Compare with the standard sizes. Match your width and length against the chart further down this page to identify the nominal size.
Inches are fine if your tape only shows imperial, but convert before you shop: UK mattresses are sold by centimetre size. The inches to cm converter does it exactly (1 inch is 2.54 cm).
What size is my mattress? Match your measurements
Your width figure usually tells you the size, because most UK lengths are either 190 cm or 200 cm. Allow a centimetre or two either way for normal manufacturing variation and wear.
| If your mattress measures about | In inches | It is probably a UK |
|---|---|---|
| 75 × 190 cm | 29.5 × 74.8 in | Small single (2ft 6in) |
| 90 × 190 cm | 35.4 × 74.8 in | Single (3ft) |
| 120 × 190 cm | 47.2 × 74.8 in | Small double (4ft) |
| 135 × 190 cm | 53.1 × 74.8 in | Double (4ft 6in) |
| 150 × 200 cm | 59.1 × 78.7 in | King (5ft) |
| 180 × 200 cm | 70.9 × 78.7 in | Super king (6ft) |
| 60 × 120 cm | 23.6 × 47.2 in | Cot |
| 70 × 140 cm | 27.6 × 55.1 in | Cot bed |
If the length is 200 cm but the width is 90 cm or 140 cm, you almost certainly have a European size (90 × 200 or 140 × 200), often supplied with Scandinavian or continental bed frames. A width of around 152 cm with a length of around 203 cm points to a US queen.
How do you measure the depth of a mattress?
Measure from the base the mattress sits on to the underside of a straight edge laid across the top. Measuring directly against the rounded border tends to under-read, especially on pillow-top and pocket-sprung mattresses with a domed top.
Depth matters most for bedding. Fitted sheets state a pocket or “box” depth on the packet, and that figure needs to be at least as deep as the mattress plus any topper, or the elastic will keep pulling off the corners. A deep sheet on a shallow mattress is less of a problem; it simply tucks under further.
How do you measure a bed frame for a new mattress?
Measure the inside of the frame, between the side rails and between the headboard and footboard, not the outside. The frame’s outer dimensions include the thickness of the timber or metal and can be 10 cm or more larger than the mattress it holds.
- Width: measure between the inner faces of the side rails at the middle of the bed.
- Length: measure from the inside of the headboard (or head rail) to the inside of the footboard. On an open-ended frame, measure the slatted area.
- Depth available: on a frame with raised side rails, measure from the slats to the top of the rail. This tells you how much of the mattress will sit inside the frame.
For a divan, the base is usually made to the same nominal size as the mattress, so measure the top surface of the base the same way you would a mattress. Remember that a standard size is nominal: a mattress sold as 135 × 190 cm and a frame sold for “a double” may still differ by a centimetre or so, which is normal.
Why does my mattress measure smaller than its label?
Rounded edges, compression and normal tolerances all make a real mattress read slightly under its nominal size. A reading a centimetre or two short of the label is not a fault.
- Border shape. Measuring over a rounded or piped edge gives a different figure from measuring the flat panel.
- Wear. Older mattresses compress where people sleep, which reduces depth more than width or length.
- Rolled mattresses. Vacuum-packed “bed in a box” mattresses need time to recover their shape after unpacking. Follow the manufacturer’s unboxing instructions and wait before measuring.
- Tolerances. Mattresses are made to nominal sizes, and the international standard ISO 24975 sets out how beds and mattresses are measured and the recommended tolerances between them.
How do you measure a cot mattress?
Measure the inside of the cot, then buy a mattress made for that size so it fits snugly with no gaps at the sides or ends. The common UK sizes are 60 × 120 cm for a cot and 70 × 140 cm for a cot bed, but some cots are made to other sizes. The NHS advises a firm, flat mattress for babies; the Lullaby Trust gives detailed safer-sleep advice, and your health visitor can help if you are unsure.
Common mistakes to avoid
- Measuring with the protector or topper still on, which adds to every dimension.
- Measuring the outside of a bed frame instead of the inside.
- Trusting the name alone; a UK “queen” or “small double” is 120 cm wide, not the same as a US queen.
- Mixing UK and European sizes: a 140 × 200 cm mattress will not sit properly in a 135 × 190 cm frame.
- Forgetting the depth when ordering fitted sheets or a new headboard height.
UK, European and US mattress sizes compared
UK lengths are 190 or 200 cm, European mattresses are usually 200 cm long, and US mattresses are made in whole inches. Use this table when a measurement does not match any UK size.
| Name | UK | Typical EU | US |
|---|---|---|---|
| Single / twin | 90 × 190 cm | 90 × 200 cm | 96.5 × 190.5 cm (38 × 75 in) |
| Double / full | 135 × 190 cm | 140 × 200 cm | 137.2 × 190.5 cm (54 × 75 in) |
| King / queen | 150 × 200 cm | 160 × 200 cm | 152.4 × 203.2 cm (60 × 80 in) |
| Super king / king | 180 × 200 cm | 180 × 200 cm | 193 × 203.2 cm (76 × 80 in) |
Frequently asked questions
Do you measure a mattress width or length first?
Either order works, but UK retailers list sizes as width × length × depth, so writing them in that order avoids confusion. A double is 135 × 190 cm.
How do I know if my mattress is a double or a king?
Measure the width and length. A UK double is about 135 by 190 cm and a UK king is about 150 by 200 cm, so a king is 15 cm wider and 10 cm longer.
Should I include the topper when measuring mattress depth?
Measure the mattress on its own to identify it, then add the topper’s thickness when you choose fitted sheets. The sheet pocket must be at least as deep as both together.
Is it normal for a mattress to measure 1 or 2 cm less than its size?
Yes. Rounded borders, compression and manufacturing tolerances mean a mattress often measures slightly under its nominal size. Measure across the middle of each face for the most reliable figure.
Can I measure a mattress in inches?
Yes, but convert to centimetres before buying, because UK mattresses are sold by metric size. Multiply inches by 2.54 to get centimetres.
Sources
- BSI: ISO 24975:2026 Beds and mattresses. Methods of measurement and recommended tolerances
- National Bed Federation (UK bed industry trade association)
- NHS: Reduce the risk of sudden infant death syndrome
- National Physical Laboratory for the definition of the inch (exactly 25.4 mm)
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