Choosing Mattresses for Bunk Beds: Depths and Sizes

The right mattress for a bunk bed is the size the frame was built for, usually a UK single at 90cm by 190cm, and no deeper than the maximum depth stated by the manufacturer. On the top bunk in particular, depth is a safety measurement rather than a comfort preference: the guard rail must rise well above the sleeping surface, which in practice usually means a mattress somewhere between 12cm and 18cm deep, depending on the frame.

Get those two numbers right and the rest comes down to support, materials and how the mattress will be used. Our range of modern mattresses UK includes single options in a variety of depths, so it is worth knowing what to look for before you choose. This guide explains why bunk bed mattresses differ from ordinary ones, how to read a frame specification and which constructions tend to work best for children.

Why Bunk Beds Need a Different Approach

On a standard bed, a deeper mattress simply sits higher. On a bunk, the top guard rail is fixed. Every extra centimetre of mattress reduces the height of the barrier above the sleeper. The British and European standard for bunk beds, BS EN 747, sets a minimum distance between the top of the mattress and the top of the guard rail, and manufacturers design their frames around a specific maximum mattress depth to meet it.

That is why most bunk bed frames carry a marking or label showing the highest point a mattress should reach. If you cannot see one, the product instructions should state the maximum depth. Treat it as a firm limit rather than a guideline. The same principle applies across our wider modern bedroom furniture UK range: the frame and the mattress should always be chosen as a pair.

The lower bunk is more flexible, but it is still worth staying close to the recommended depth. A very thick mattress on the bottom can reduce headroom between bunks and make it awkward for a child to sit up in bed.

Standard UK Sizes for Bunk Bed Mattresses

Most frames in the UK use one of the following sizes:

• Single: 90cm by 190cm. By far the most common size for both bunks.
• Small single: 75cm by 190cm. Found on compact or space saving frames.
• Short or junior: around 70cm by 140cm or 160cm. Used on toddler and junior bunk beds.
• Small double: 120cm by 190cm. Sometimes used on the lower level of triple bunks or larger family bunks.

Continental or imported frames can occasionally use European sizes such as 90cm by 200cm. A mattress that is too short leaves a gap where small limbs can become trapped, and one that is too long simply will not fit. Always match the mattress to the internal dimensions of the frame rather than relying on the name of the size.

If you are still deciding on the frame itself, our modern bunk beds UK collection lists the mattress size each design takes, which makes pairing straightforward. The same applies to cabin beds and other frames in our modern children’s beds UK range.

Understanding Mattress Depth

Depth is measured from the base of the mattress to the top of the sleeping surface, including any quilting or pillow top. This is where many families get caught out. A mattress advertised at 15cm may in reality measure a little more once the cover is filled out, so check product dimensions carefully and measure on arrival.

As a general picture:

• Thinner mattresses, around 10cm to 12cm, suit lightweight young children and frames with low guard rails.
• Medium depths, around 14cm to 18cm, are the most common choice for children and teenagers and give a good balance of comfort and safety on most frames.
• Deeper mattresses, 20cm and over, are rarely suitable for the top bunk and are better kept for the lower level, where the frame allows.

If two children of different ages share the bunk, you can use different depths on each level. The older child on top may still need a slim mattress for safety reasons, while a younger sibling below can have something a little deeper if the frame permits.

Which Mattress Constructions Work Best

Open coil

Open coil mattresses use a connected network of springs. They are light, breathable and easy to lift, which helps when making the top bunk. They suit younger children who will grow out of their mattress relatively quickly.

Pocket sprung

Pocket springs are individually wrapped, so they move independently and give more targeted support. Shallow pocket sprung mattresses designed for bunk beds are a good choice for older children and teenagers, whose weight and sleeping positions put more demand on the mattress.

Foam and memory foam

Foam mattresses can offer good support in a slim profile, which makes them well suited to bunk beds. Memory foam moulds to the body, though some children find it warm. Reflex or high density foam tends to feel cooler and springier. Our guide to how mattress firmness labels compare in UK testing explains why firmness descriptions vary between brands.

Hybrid

Hybrids combine springs with foam layers. Many are too deep for a top bunk, but some slimline versions are designed specifically for children’s beds.

Firmness for Growing Children

Children generally do best on a medium to medium firm mattress. Their bodies are lighter than an adult’s, so a very soft mattress offers little support, while a very firm one can feel uncomfortable on hips and shoulders. A medium surface keeps the spine in a natural position and is comfortable for a range of sleeping styles.

For teenagers, who can be close to adult weight, a slightly firmer pocket sprung mattress usually lasts better. If your teenager is moving from a bunk to a full single bed of their own, our article on upholstered single beds for UK children and teenagers is a useful next step.

Practical Features Worth Looking For

• A removable, washable cover. Spills and accidents happen, and being able to wash the cover makes the mattress last longer.
• Breathable materials. The top bunk sits closer to the ceiling, where warm air collects. Breathable fillings help keep things comfortable.
• Fire safety compliance. Mattresses sold in the UK should meet the relevant fire safety regulations. Look for the appropriate label.
• Manageable weight. You will be lifting the top mattress to change sheets. A lighter mattress makes this far easier.
• Side handles. Small handles help you turn and position the mattress without straining.

Bedding and Mattress Protectors

A waterproof mattress protector is one of the most useful things you can buy for a child’s bed. Choose a breathable, quiet design so it does not rustle or trap heat. Fitted sheets should match the depth of the mattress, so avoid deep fitted sheets on slim bunk mattresses, as the excess fabric can bunch and create an uneven surface.

On the top bunk, keep bedding simple. A single duvet and one pillow are usually enough. Bulky throws and stacks of cushions take up headroom and can end up on the floor below.

Caring for a Bunk Bed Mattress

Rotate the mattress head to foot every few months to even out wear. Many children’s mattresses are single sided, so check before flipping. Air the mattress when you change the bedding and vacuum it occasionally to remove dust.

Make sure the slats underneath are evenly spaced and in good condition. A broken or missing slat can cause the mattress to sag, which affects comfort and, on the top bunk, raises the sleeping surface unevenly.

Measuring a Mattress You Already Own

If you are hoping to reuse an existing single mattress on a new bunk, measure it before assuming it will fit. Lay it flat on the floor and measure the length and width at the centre, then measure the depth at the edge, pressing gently on any quilted top to find its true height. Compare all three figures with the frame specification. A mattress that has been in use for some years may also have softened or developed a slight dip, which affects comfort more noticeably on a raised bed where a child cannot easily shift position. If in doubt, reserve an older mattress for the lower bunk and choose a fresh, slimmer one for the top.

When to Replace It

Children’s mattresses tend to need replacing when a child moves to a noticeably larger size or weight, or when the mattress shows visible dips and no longer recovers its shape. If your child is waking with aches or complaining that the bed is uncomfortable, it is worth a closer look.

Choosing a bunk bed mattress is a simple process once you know the frame’s size and maximum depth. Stay within those limits, pick a medium support level and look for practical details like a washable cover. To explore beds, mattresses and coordinating children’s furniture together, visit Furniture in Fashion.

Frequently Asked Questions

Can I use a normal single mattress on a bunk bed?

You can if its size matches the frame and its depth is within the manufacturer’s stated maximum. Many standard single mattresses are too deep for the top bunk.

How deep should a top bunk mattress be?

It depends on the frame, but most top bunks are designed for mattresses roughly 12cm to 18cm deep. Always follow the maximum depth marked on the frame.

Do bunk beds need special mattresses?

Not necessarily. They need mattresses of the right size and depth. Some mattresses are marketed for bunk beds because they are made in slimmer profiles.

Should both bunks have the same mattress?

Not always. The top bunk is limited by guard rail height, while the bottom bunk can sometimes take a slightly deeper mattress if the frame allows.