Buying a mattress for a bunk bed isn't the same as buying one for a normal bed. The top bunk usually needs a mattress no deeper than 15 or 16cm, so the guard rail still works properly. The bottom bunk has more flexibility, and a trundle needs a slim mattress of around 10cm to slide underneath. Here's everything in one place: depth, sizes, how many you need, and the mistakes to avoid.
15 to 16cm
The usual maximum depth for a top bunk
Around 10cm
What a trundle mattress needs to slide away
2 or 3
Mattresses for a bunk bed, or one with a trundle
On this page
Depth is a safety figure, not a preference
The top bunk of a bunk bed takes a maximum mattress depth, usually 15 or 16cm. Guard rails are designed to sit a set height above the mattress surface, and that height is what stops a child rolling over the rail. Most high-street single mattresses are 20cm or deeper, so putting one on a top bunk takes 5cm or more off the rail's effective height. The rail is still there; it just isn't doing what it was designed to do.
Check your bed's stated maximum before you order. It's on the product page, and it varies between models because each manufacturer sets it for their own rail height.
The bottom bunk has no guard rail above its mattress, so it's more flexible, but a very deep mattress eats into the headroom under the top bunk, so check the product page. In practice, most families buy two identical mattresses, which is simpler and means the children aren't sleeping on noticeably different beds.
A trundle is different again. Its mattress has to clear the underside of the bed above when it slides away, which usually means around 10cm. A standard mattress physically won't fit.
How many do you need?
| Bed | Mattresses |
|---|---|
| Standard bunk bed | Two, both within the top bunk's depth limit |
| Bunk bed with a trundle | Three: two for the bunks, one slim one for the trundle |
| Triple bunk bed | Three |
| Family bunk with a double bottom | Two: a double or small double, depending on the bed, and a single |
| Family bunk with a trundle | Three |
| Quadruple bunk | Four |
This is the most commonly forgotten part of a bunk bed order. The bed arrives, gets built, and there's nothing to sleep on.
Which size?
Most bunk beds take a standard UK single, 90 x 190cm. Three exceptions are worth knowing:
- Shorty bunks take 75 x 175cm. A standard single is 15cm too long and won't fit.
- Continental bunks take 90 x 200cm. A 190cm mattress leaves a gap at the end, which is uncomfortable, and on a raised bed a gap is an entrapment risk.
- Family or double bunks take a double or small double on the bottom, depending on the bed, and a single on top. See our double bunk bed guide.
The bed's product page states the mattress size it needs, so work from that rather than measuring the frame, which is always larger than the mattress. Our kids' mattress size guide lists every size.
Our 15cm range
All made in the UK and built to 15cm for bunk beds, high sleepers and mid sleepers. They arrive vacuum packed and rolled, so they're far easier to get up a ladder.
15cm, memory foam
MemoryDream 15
Contours to the body and stays quiet, which matters on a bunk: springs on the top bunk can be heard from the bottom. The one most parents choose.
Sizes and details
15cm, pocket sprung
PocketRest 15
Springs let more air through, so it sleeps cooler. Worth considering for the top bunk, which is usually a little warmer.
Sizes and details
15cm, reflex foam
ComfortSleep 15
A medium feel and our best-value option. Good for younger children and a bottom bunk that gets occasional use.
Sizes and details
10cm, for trundles
TrundleEase 10
Built slim enough to clear the frame when the trundle slides back under the bed.
Sizes and detailsFor bedwetting, the DryComfort 15 is fully waterproof at the same 15cm depth. See all bunk bed mattresses, or compare them in our guide to the best single mattress for kids.
Should the two mattresses be the same?
Usually, yes. Matching mattresses avoid complaints when children swap bunks, and if one is noticeably better than the other, you'll hear about it. Where it's worth choosing differently:
- The top bunk sleeps hot. A pocket sprung mattress on top and foam underneath is a sensible split. A lighter duvet on the top bunk helps too; see our guide to room temperature and sleep.
- A big age gap. A younger, lighter child and a teenager may prefer different feels.
- Budget. If the bottom bunk is mostly for sleepovers, a ComfortSleep underneath and a MemoryDream on top is a sensible way to split the spend.
Things that catch people out
- Buying one mattress. The bed price almost never includes them, and a bunk needs two, or three with a trundle.
- Assuming a standard single fits a shorty bunk. It's 15cm too long.
- Using a high-street mattress on the top bunk. Almost all are 20cm or deeper. That lowers the rail's effective height and eats into the headroom between the child and the ceiling.
- A standard mattress on a trundle. It won't slide away, and you'll only find out once it's unrolled.
- Forgetting the protector. Cleaning a mattress on a top bunk is genuinely difficult, so a waterproof protector matters most up there. If there is an accident, take the mattress down to the floor to clean it; our guide to urine smell explains how.
Getting it up there
A rolled mattress is far easier to carry upstairs and lift onto a top bunk than a flat one. Lift it up rolled, then unwrap it on the bunk. Allow 24 to 48 hours for it to fully expand before making the bed; it will look thinner than expected for the first few hours.
Before you order
- Check the maximum mattress depth on the bed's product page.
- Check the mattress size the bed needs: single, shorty, continental or double.
- Count them: two, or three with a trundle.
- Add protectors. They're cheaper than a new mattress, and far easier than cleaning one at height.
- Order the mattresses with the bed, so everything arrives together.
Common questions
What depth mattress for a bunk bed?
Usually 15 or 16cm at most on the top bunk. Check your bed's product page for the exact figure.
Why does bunk bed mattress depth matter?
Guard rails sit a set height above the mattress surface. A deeper mattress reduces that height, so the rail is less effective at stopping a child rolling out.
Can I use a thicker mattress on the bottom bunk?
Often, yes, as there's no guard rail above it, but check the product page, because a deep mattress reduces headroom under the top bunk. Most families buy two identical mattresses anyway.
What size mattress does a bunk bed take?
Most take a standard UK single, 90 x 190cm. Shorty bunks take 75 x 175cm and continental bunks take 90 x 200cm. Family bunks take a double or small double on the bottom.
How many mattresses do I need for a bunk bed?
Two, or three if it has a trundle, with the trundle one slimmer at around 10cm. A triple bunk needs three.
What mattress fits a trundle bed?
A slim one, around 10cm deep, so it clears the frame above when it slides away. A standard mattress won't fit.
Foam or sprung for a bunk bed?
Foam is quieter, which matters when someone is sleeping underneath. Sprung sleeps cooler, which matters more on the top bunk. Either works.
Are 15cm mattresses comfortable enough?
Yes, for a child. Depth and comfort aren't the same thing, and a well-made 15cm mattress supports a child perfectly well. The extra depth in an adult mattress is there for adult body weight.
Mattresses made for bunk beds
UK-made, 15cm deep, rolled for easy delivery, plus slim trundle mattresses.
Shop bunk bed mattressesBuying the bed too? Read our bunk bed buying guide or browse all bunk beds.
