Getting the size wrong is the most expensive mistake in buying a child's bed, because you usually don't find out until it's built.
This guide covers every size we sell, when to move up, and the two measurements that catch people out.
UK bed and mattress sizes
| Size | Mattress dimensions | Typical age |
|---|---|---|
| Cot bed | 70 x 140cm | Up to 4 or 5 |
| Shorty | 75 x 175cm | 4 to 8 |
| Small single | 75 x 190cm | 4 upwards |
| Single | 90 x 190cm | 6 upwards |
| Continental single | 90 x 200cm | Teens |
| Small double | 120 x 190cm | Teens, or sharing |
| Continental small double | 120 x 200cm | Teens |
| Double | 135 x 190cm | Teens and adults |
| Continental double | 140 x 200cm | Teens and adults |
The bed frame itself is larger than the mattress, usually by 5 to 10cm on each side. Always work from the frame's overall dimensions when you're measuring a room, not the mattress size.
The size most people don't know exists
Shorty, 75 x 175cm. It's 15cm shorter and 15cm narrower than a standard single, which sounds trivial and isn't. In a small box room it's often the difference between the bed fitting and not.
It suits roughly ages 4 to 8, so it buys three or four years. The trade-off is that it's an extra size along the way, so if the room allows it, going straight from a cot bed to a standard single saves a purchase.
The thing to watch: a shorty bed needs a shorty mattress. A standard single won't fit, and it's an easy and expensive mistake. We stock shorty mattresses in the correct size, which many retailers don't.
Continental sizes explained
Continental sizes are 200cm long rather than 190cm. That extra 10cm matters more than it sounds once a child hits their teens, and it costs nothing extra in floor space that a growing teenager won't use.
The catch is that a continental bed needs a continental mattress. A standard 190cm mattress leaves a 10cm gap at the end, which is both uncomfortable and, on a raised bed, an entrapment risk.
If you're buying for a child who's already tall for their age, it's worth going continental now rather than replacing at fourteen.
When to move up a size
Forget age brackets. Use the bed itself.
The 10cm rule. Measure from the top of your child's head to the end of the mattress while they're lying flat. Once there's less than 10cm, you've got roughly a year left.
Other signs:
- They sleep diagonally, or with feet hanging over
- They wake up against the side of the bed regularly
- They've stopped wanting to be in it, which is often about space rather than the bed
Children grow in bursts rather than steadily, so a bed that fitted at the start of the school year often doesn't by the summer.
Mattress depth: the one that catches people out
Size isn't the only measurement that matters. On any raised bed, depth is a safety figure.
Bunk beds, high sleepers and mid sleepers have a maximum mattress depth, usually 15 or 16cm. Guard rails are designed to sit a set height above the mattress surface. Most high-street single mattresses are 20cm or deeper, which removes 5cm of guard rail and stops it doing its job.
Trundle beds have their own limit, usually around 10cm, because the mattress has to clear the frame above when it slides away.
Everything in our bunk bed mattress range is built at 15cm for this reason. Check the maximum depth on your bed's product page before ordering anything.
Matching size to room
Small rooms, under about 2.5 x 2.5m
A shorty or small single frees up meaningful floor space. If ceiling height allows and your child is 6 or over, a high sleeper is the bigger gain, because the bed goes up and the floor comes back.
Under 6, a mid sleeper or cabin bed does the same job at a safer height.
Average rooms
A standard single with storage underneath is the most useful bed you can buy for the money, and it lasts from six through to the teens.
Shared rooms
A bunk bed sleeps two in the footprint of one. If the ceiling is low or the younger child is under 6, look at low bunks specifically. Our guide to low bunk beds covers the differences.
Sleepovers
A trundle bed looks like a single and pulls out into two. It takes one bed's worth of floor space the rest of the time, which is the whole point.
Before you order
- Measure the room, including ceiling height directly above where the bed will stand.
- Work from the frame dimensions, not the mattress size. The frame is bigger.
- Check the ladder projection on any bunk or raised bed. It isn't always in the headline dimensions.
- Check the maximum mattress depth if it's a raised bed.
- Count the mattresses. A bunk needs two. A bunk with a trundle needs three.
Not sure? Message us with the room dimensions and your child's age and we'll tell you what fits.
Common questions
What size bed does a 4 year old need?
A shorty, small single or standard single all work. A standard single lasts longest; a shorty fits a small room better.
What's the difference between a shorty and a small single?
Length. A shorty is 175cm, a small single is 190cm. Both are 75cm wide.
Can I put a standard single mattress on a shorty bed?
No, it's 15cm too long. Shorty beds need shorty mattresses at 75 x 175cm.
What is a continental size?
200cm long instead of 190cm. Common on European-made beds and worth having for a taller child or teenager. It needs a continental mattress to match.
When should my child move to a full-size single?
When there's less than 10cm between their head and the end of the mattress, or when they start sleeping diagonally. Usually somewhere between six and nine.
What mattress depth do I need for a bunk bed?
Check your specific bed, but it's usually a 15 or 16cm maximum. Deeper reduces the guard rail clearance.
Is a small double too big for a child?
Not if the room takes it. At 120 x 190cm it's a good option for a teenager, or for a child who'll have friends staying.
Still deciding what type of bed rather than what size? Read our kids' bed buying guide.
