A cot bed measures 70 × 140 cm (about 27.5 × 55 in) and takes a 70 × 140 cm mattress, while a standard cot is 60 × 120 cm and takes a 60 × 120 cm mattress.
Buy the wrong mattress and the gap along the rails is the whole problem: a mattress that shifts or leaves a wide opening lets a baby’s arm or leg slip through and get trapped. Cot beds and standard cots look similar in a photo, which is why so many parents order the wrong sheet or mattress, then discover the mismatch only after unboxing. Below: both sizes, the fit tolerance that keeps a mattress safe, and the thickness limit that catches people out. The sizing standards are UK and European, so treat them as a reference point and always measure your own furniture before buying.
Cot Bed vs Standard Cot: How The Two Sizes Differ
A cot bed, at 70 × 140 cm, is larger and usually converts into a toddler bed; a standard cot is smaller, at 60 × 120 cm, and typically stays a cot.
Both take their own mattress size, and the two are not interchangeable. Putting a 60 × 120 cm mattress in a 70 × 140 cm cot bed leaves roughly 10 cm of slack along the length and 10 cm along the width — far past any safe fit. Match the mattress to the furniture’s actual internal dimensions, not the label on the box.
If you’re stocking up on bedding, the fitted sheets sold for the cot bedsheets worth buying are sized to these same two footprints, so a 70 × 140 cm sheet will not stay put on a 60 × 120 cm mattress.
How To Measure Your Cot Before You Buy A Mattress
Measure the inside of the cot frame — rail to rail and headboard to footboard — and buy a mattress that matches that internal size within about 1 cm. Manufacturer guidance cites an internal width of roughly 600–610 mm and length of 1200–1210 mm for cot mattresses; roughly 700–710 mm by 1400–1410 mm for cot-bed mattresses. Those narrow ranges leave only a sliver of play.
Two rules govern whether the mattress fits:
| Furniture Type | Mattress Size | Notes |
|---|---|---|
| Standard cot | 60 × 120 cm | Smaller footprint; stays a cot |
| Cot bed | 70 × 140 cm (≈ 27.5 × 55 in) | Converts to a toddler bed |
| US full-size crib | ≈ 28 × 52 in | Thickness cap ≈ 6 in |
| Cot mattress internal width | ≈ 600–610 mm | Match to cot frame |
| Cot-bed mattress internal width | ≈ 700–710 mm | Match to cot-bed frame |
| Maximum safe side gap | 3 cm | Larger gaps risk entrapment |
| Max cot mattress depth | 10 cm | Per British cot guidance |
Why The Fit Matters More Than The Number On The Label
A mattress that’s too small is a safety problem, not just cosmetic: cot fit guidance warns that a loose mattress lets a child trap an arm or leg in the gap, and the 3 cm limit exists for that reason. Fit also decides whether bedding works — a correctly sized mattress holds a fitted sheet taut instead of letting it bunch under a sleeping baby.
Standard mattress guides note that cot and cot-bed sizes are frequently confused at the point of sale, which is why buying by name alone goes wrong. Take your cot’s internal measurements, compare them against the 60 × 120 cm and 70 × 140 cm standards, and buy to whichever your frame matches. For US shoppers, verify against the crib standard separately — the cot-bed sizing above is UK and European, and the two regions do not share a mattress size.
FAQs
Is a cot bed the same size as a cot?
No. A cot bed is larger, at 70 × 140 cm, while a standard cot is 60 × 120 cm. They take different mattresses and are not interchangeable, so a mattress bought for one will not fit the other. Always measure your own furniture’s internal dimensions before ordering.
How much gap is safe between a mattress and the cot sides?
Anything wider creates a space where a baby’s arm or leg can become trapped. If your mattress slides easily or leaves a visible opening along the rail, it is the wrong size for that cot.
Can I use a US crib mattress in a UK cot bed?
No. A US full-size crib mattress is about 28 × 52 inches, which does not match the 70 × 140 cm cot-bed standard. The regions use different sizing systems, so a mattress made for one will not fit the other safely. Match the mattress to your specific furniture.
References & Sources
- Sealy. “Ultimate Guide to Cot Mattress Sizes.” Source for standard cot (60 × 120 cm) and cot-bed (70 × 140 cm) mattress dimensions.
- Dreams. “The Mattress Size Guide.” Source for cot and cot-bed size comparisons and common sizing confusion.
- Happy Beds. “Bed Sizes.” Source for cot-bed sizing and fit guidance.
