What Size Is a Cot Mattress? Standard UK Cot and Cot Bed Dimensions Explained

Whether you’re setting up a nursery or checking a hand-me-down cot, the questions start quickly. What size is a standard cot mattress? Is a cot bed mattress bigger? Are all baby mattresses the same size? The short answer is that UK cots are fairly standard, but the cot bed, crib and Moses basket world is not, and a mattress that is a few centimetres too small is a real safety issue. This guide explains the standard cot mattress size, the cot bed mattress size, how cribs and Moses baskets differ, how thick a mattress should be, and exactly how to measure so you know what a safe fit looks like.

Quick Answer

A standard UK cot mattress is 120 x 60 cm, and a standard UK cot bed mattress is usually 140 x 70 cm. Both are normally around 10 cm thick. Some cot beds are smaller and take a 120 x 60 cm mattress, so always check your cot bed’s own instructions or measure the inside of the frame. A mattress should fit snugly, with no more than a 3 cm gap between the mattress edge and the sides of the cot. Cribs, Moses baskets and travel cots use different, smaller sizes.

Cot and Cot Bed Mattress Sizes at a Glance

Measurements are given as length x width. “60 x 120” and “120 x 60” mean the same mattress.

What Is the Standard Cot Mattress Size?

The standard UK cot mattress size is 120 cm long and 60 cm wide. Most mainstream cots are built to take this size, so it is the one you’ll see sold as a “cot mattress” in most shops. Dimensions are listed as length first, then width, then thickness, for example 120 x 60 x 10 cm. Babymore’s mattress guide gives the same standard sizes: 120 x 60 cm for a cot and 140 x 70 cm for a cot bed.

If you’re searching for a “60×120 cot mattress” or a “120 x 60 cot mattress”, you’re looking for the same thing. We have a dedicated guide to the 120 x 60 cm cot mattress with every option in this size.

What Is the Standard Cot Bed Mattress Size?

Most cot beds take a 140 x 70 cm mattress. That is larger than a standard cot because a cot bed is designed to last longer, converting into a toddler bed.

Not every cot bed is 140 x 70 cm. Some compact cot beds take the smaller 120 x 60 cm mattress. For example, Babymore’s Iris Cot Bed takes a 120 x 60 cm mattress, which is not included. So never buy a mattress by the words “cot bed” alone. Check the mattress size listed for your own cot bed.

How to Measure for a Cot or Cot Bed Mattress

Take five minutes to measure properly:

1. Measure inside the frame. Use the inside length and width of the cot, from the inside of the end panels and the inside of the side rails, with the base fitted.
2. Check the manufacturer’s instructions. The mattress size is usually printed in the manual or on the product page.
3. Measure from the base up. Check there’s room for a mattress about 10 cm thick, with the base at its right height.
4. Compare to the mattress you’re buying. The mattress should match the frame size.
5. Check the corners. Some cots have curved corners or an unusual shape, so make sure the mattress fits snugly all the way round.

Not sure which cot bed you have? Our guide to choosing the right cot bed explains the differences.

How Snug Should the Fit Be? The 3 cm Rule

A cot mattress should fit snugly, with no gaps where a baby’s limbs, head or face could get trapped. Babymore’s guidance is that there should be no more than a 3 cm gap between the edge of the mattress and the sides of the cot.

A quick test: push the mattress hard into one corner of the cot, then measure the gap on the opposite sides. Do the same on the other corner. If the gap is bigger than 3 cm anywhere, the mattress is too small. A mattress that is too big is no better, because it can curl up at the edges and leave the surface uneven.

If your cot is a non-standard or non-UK size, you may need a custom-sized mattress.

How Thick Should a Cot Mattress Be?

Most cot and cot bed mattresses are around 10 cm thick. Babymore’s mattress guide advises that about 10 cm gives good support and holds its shape, that mattresses of 7 to 8 cm are better kept for occasional use, and that a mattress shouldn’t be more than 10 cm deep, so it doesn’t leave too small a gap between the mattress and the top of the cot sides.

Look for a mattress made to BS EN 16890:2017, the standard for mattresses for cots. For more on what a mattress is made of and what suits your baby, see our mattress guide, and read about the different options in TYPES OF BABY MATTRESS and WHAT ARE BABY MATTRESSES MADE OF.

Cot vs Cot Bed vs Crib: Which Mattress Fits?

Cribs and Moses baskets have no standard mattress size, so always use the mattress made for yours. For example, Babymore’s Air Motion Gliding Crib comes with its own fibre mattress and takes a replacement of the same size. Do not use a standard cot mattress in a crib. For more on choosing between them, read our guide to Moses basket vs crib and the difference between a cot and a cot bed.

Are All Baby Mattresses the Same Size?

No. Cot mattresses in the UK are fairly standard at 120 x 60 cm, and cot bed mattresses at 140 x 70 cm. Beyond that, sizes vary:

• Cribs and Moses baskets are built to many different sizes.
• Travel cots have their own mattress sizes.
• Designer cots and cot beds can have non-standard dimensions, which is why you should check the exact mattress size.
• Cots made outside the UK may use different sizes. A US crib mattress, for example, is a different shape and size and won’t fit a UK cot properly.

Where These Sizes Show Up in Babymore’s Range

For reference, Babymore’s cot mattresses come in three sizes: 120 x 60 cm, 140 x 70 cm and a smaller 100 x 50 cm. All four ranges are available in the standard cot and cot bed sizes:

The Eco Fibre range also comes in a smaller 100 x 50 cm size for smaller cots. Browse all cot mattresses, cot bed mattresses or the full baby mattress range. The pocket sprung cot mattress page explains what’s inside one.

Checklist: Before You Buy a Cot or Cot Bed Mattress

• ☐ I’ve measured the inside of my cot or cot bed.
• ☐ I’ve checked the mattress size in the cot’s instructions.
• ☐ The mattress is the same size as the cot, with no more than a 3 cm gap at any edge.
• ☐ The mattress is about 10 cm thick, and no thicker.
• ☐ It meets BS EN 16890:2017.
• ☐ The mattress is new, not second-hand.
• ☐ I know whether the cot comes with a mattress or if I need to buy one.

Setting up the nursery? Our nursery furniture checklist covers the rest, and our guide to cot bed safety covers safe set-up. If you are assembling the room, our guide to assembling nursery furniture can help with the next steps.

Final Thoughts

For most UK families, the numbers to remember are 120 x 60 cm for a cot and 140 x 70 cm for a cot bed, around 10 cm thick, with no more than a 3 cm gap at the edges. But the cot’s own instructions always come first, because not every cot bed follows the standard. Measure, check, and match the mattress to the frame.

Want to go further? Our mattress guide explains firmness, materials and safety standards, and our cot mattresses and cot bed mattresses pages list what is available in each size.

Frequently Asked Questions