What do you know about your bunk so far?
- I've found the maximum-mattress mark
- There's no mark or instructions
- I'm not sure the mattress fills the base
- It's second-hand and I want to check it
- An adult will be sleeping on it
Keep the mattress at or below the bed's maximum-mattress mark
Use the bed's maximum-mattress mark and instructions to find the mattress depth allowed for your bunk. The guard rail only protects while enough of it stands above the sleeping surface. Adding depth reduces that height, even when the mattress feels comfortable and fits neatly across the base.
In its guidance for landlords, Lewisham Council Trading Standards says the top of the guard rail must be at least 260 mm above the top of the bed base.3 It also says the top of the mattress must be at least 160 mm below the top of the guard rail. The bed's own marked maximum is the mattress limit.
The authors of a single-centre German study published in 2022 suggest, in their discussion citing other work, using mattresses recommended by the manufacturer so that enough guard rail remains above the mattress to help prevent falls from the upper bunk.5 I think following the maker's recommendation is the simplest place to start, provided you have the details for your particular bed.
We asked Jim Oram why the thickness of a top bunk mattress makes a difference. He is a home safety policy officer at the Royal Society for the Prevention of Accidents (RoSPA), and RoSPA sent his answers by email in October 2026.
Find the maximum-mattress mark on your bed before you shop and write the number down. That number is the only depth limit you buy by. Compare the depth on the mattress listing with it, and if the listing gives no depth, or only a range, ask the mattress seller for the exact figure before you order. A thinner mattress than you expected is fine, as long as it's within that limit.
If the maximum-mattress mark is missing, ask the maker first
A missing mark or missing instructions means you need more information before buying. Ask the maker or seller for the mattress requirements for that model. A second-hand or discontinued bunk might take more tracing, so use any model details on the bed to help identify it.
If neither the maker nor the seller can give you that figure, you have no safe limit for that bed. Don't guess one. A general clearance figure is not a substitute, so don't buy a mattress for that bed until you have the number. Lewisham's figures still apply to the bed itself. If the guard rail stands less than 260 mm above the base, the bed falls short of Lewisham's guidance whatever mattress you put on it.
Once the new mattress is on, check it sits flat and fills the base. For a rolled mattress, wait until it has had the maker's full expansion time, because it stands taller once it has finished expanding.
Buy the bunk mattress size the maker states, with no gaps
Buy the mattress size the bunk bed's maker states, with no gap beside the guard rail or at the ends. A mattress smaller than the base leaves somewhere your child can slip into. If you're unsure about the fit, measure the base and compare it with the maker's stated size before ordering.
A mattress you already own still needs to meet those requirements. Don't assume it will fit because it came from another bunk bed or because its size description sounds familiar. The actual fit on your bed matters, and I'd buy your child a proper new mattress in the size required.
Never add a second mattress, a topper or extra padding on a top bunk, for any reason. Each raises the sleeping surface towards the top of the guard rail. If the mattress feels uncomfortable, look for a replacement that meets the bed's requirements instead of adding a layer.
The bottom bunk needs a suitable fit too, so follow the bed's instructions for it. Use a fitted sheet that fits the mattress snugly. A sheet intended for a much deeper mattress will leave loose fabric around a thinner one.
The top bunk isn't for under-sixes or children who sleepwalk
Keep children under six and children who sleepwalk off the top bunk. The Child Accident Prevention Trust says children can have serious falls from the tops of bunk beds and doesn't recommend the top bunk for children under six.1 It also says to teach children not to play on the top bunk.
In Macgregor's 2000 study, 85 children attended one UK children's A&E department over five months following falls from beds or top bunks. Of the injuries, 66, or 78%, were in children under six.4 Beds and top bunks were pooled. The author concluded that children under six should not sleep in upper bunks.
The NHS advice on sleepwalking says not to let your child sleep in the top of a bunk bed if they sleepwalk.2 If your child sleepwalks, arrange a sleeping place away from the top bunk. Jim Oram's advice for RoSPA on when a child is ready for the top bunk is in our guide to bunk beds.
Read the bed's markings and instructions before choosing a mattress
Check the bed itself before you order its mattress, including its markings and instructions. Lewisham Council Trading Standards' guidance says bunk beds should comply with BS EN 747. Look for that information when choosing the bed, alongside its mattress requirements.
Follow the instructions for assembly and fixing, including any requirement to fix the bed to a wall, and for the ladder. Reading them before the flat-pack becomes a jigsaw is time well spent. You also need to check any weight limit stated for the bed. That applies to children and adults alike.
The Office for Product Safety and Standards reported that a bunk bed recalled in 2024 had failed testing because gaps between its base slats were wider than the maximum and required information and warnings were missing.6 That's a practical reason to look at the bed and its paperwork as carefully as you look at the mattress.
Once you've established the required fit, you can compare what the mattress is made of. Our children's mattress guide and teenager mattress guide cover construction and comfort. Keep your bunk's size and depth requirements beside you as you compare options, because a comfortable mattress still needs to fit the bed it's for.
- I've found the bed's maximum-mattress mark and noted it
- The seller has given me the mattress's exact depth
- That depth is at or below the mark
- The mattress is the size the bunk's maker states
- No topper or extra padding will go on the top bunk
- Nobody under six, or who sleepwalks, will sleep up top
Avoid mattresses and arrangements that reduce bunk safety
- A mattress deeper than the bed's maximum-mattress mark. It reduces the height of the guard rail above the sleeping surface.
- A mattress smaller than the base. Gaps beside the guard rail or at the ends leave somewhere your child can slip into.
- A second mattress, topper or extra padding on the top bunk. These raise the sleeping surface towards the top of the guard rail.
- A child under six or a child who sleepwalks on the top bunk. Follow the Child Accident Prevention Trust's age recommendation and the NHS advice on sleepwalking.
- Letting your child play or climb on the top bunk. Teach your child that the top bunk is for sleeping and how to use the ladder according to the bed's instructions.
Bunk bed safety advice
The Child Accident Prevention Trust says: "Children can have serious falls from the tops of bunk beds. That's why we don't recommend the top bunk for children under six. Teach children not to play on the top bunk."
NHS advice on sleepwalking says: do not let your child sleep in the top of a bunk bed if they sleepwalk.
In its guidance for landlords, Lewisham Council Trading Standards says: "The distance between the upper edges of the safety barrier of the top bed and the upper side of the bed base must be at least 260mm. The top of the mattress must be at least 160mm below the upper edge of the safety barrier."
