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A Guide to Kids’ Mattress Sizes & Bed Sizes

The Ultimate Guide to Kids’ Mattress Sizes & Bed Sizes

When finding the perfect bed for your child, you want to make sure you choose a size that allows plenty of space for growth. Kids grow so quickly, and you don’t want to have to replace their bed every time they do! To make it a worthwhile investment, it always helps to leave room to grow.

A bed and mattress that are too small or too big for your child will impact their sleep hygiene, which can lead to development and growth issues, so it’s important to know what kids’ bed size and mattress size is most suitable.

UK Kids’ Mattress Sizes

Use the following chart to guide your kids’ mattress search:

Bed Type

Mattress Size

Recommended Age


L 120cm x W 60cm

0 – 2 years old

Cot Bed

L 140cm x W 70cm

2 – 4 years old

Small Single

L 191cm x W 76cm

4+ years old


L 191cm x W 90cm

4+ years old

Small Double

L 191cm x W 120cm

8+ years old

These are averages, but exact measurements may vary, so when considering child’s mattress size make sure you look at the specific dimensions for the mattress that you’re interested in.

Mattress depth can vary, and the best mattresses for children will be thinner than full-sized mattresses.

When to Transition Beds

From baby to toddler

It’s recommended that babies use cots from 0 to 2 years old, before moving to a toddler or cot bed. Cots are perfect for newborn babies, with protective railings and plenty of space to grow, but once they start to get bigger, you’ll want to upsize to ensure they’re comfortable.

Cot beds and toddler beds are perfect for transitioning towards larger kids’ beds. They’re more spacious than a cot for newborns and designed more like a regular bed, but with essential safety measures in place. Cot beds and toddler beds do require specific mattresses.

From toddler to preschool

Generally, little ones outgrow their cot or toddler bed at around 4 years old, and at that point they can move up to a small single. You could choose to go for a standard single bed at this age, but small singles still provide plenty of room for growth while saving you a bit of space in their room.

From age 4 onwards, it really comes down to their personal growth; you might choose to move them to a standard single bed if they’re growing quickly or stick with a smaller single until they’re nearing double digits. So long as they have space to grow and they’re comfortable – you don’t need to rush into upsizing.

Transitioning to adolescence

From age 8 and up is when they’ll likely start to hit some significant growth spurts, and at this time you might consider moving them to a small double bed to ensure their comfort. Once they get close to adolescence, it’s so important they have a supportive, spacious bed.

Bunk Bed Mattress Sizes

If your children share a room with a bunk bed, it’s really important that you use mattresses specifically designed for bunks. There are some safety risks involved with bunk beds and using a specially designed mattress ensures their thickness and weight won’t pose any risks.

While the width and length of a bunk bed mattress remains the same as a regular bed – a single bunk bed mattress measures 191cm x 90cm – the depth of a bunk bed mattress must not exceed 17cm.

Bunk bed mattresses should be thinner and lighter than the average kids’ mattress. Explore our range of bunk bed mattresses to ensure both complete safety and complete comfort for your little ones.

Trundle and Futon Mattress Sizes

Like bunk beds, trundles need specific mattresses as they need to fit neatly underneath a full-sized bed. The same goes for futons, which need to be able to nicely fold into a seat when not being used as a bed. We have a range of trundle mattresses and futon mattresses at Aspace, designed with practicality and comfort in mind.

Single trundle mattresses typically measure 183cm x 77cm with a depth of no more than 14cm, but the size can vary. We also offer trundle bed mattresses that are 183cm x 90cm. Our futon mattresses are 190cm in length and between 75cm and 80cm in width depending on the style you choose.  

The Best Kids’ Bed Size to Save Space

Of course, the size of their room factors into the equation. As kids grow and start to explore their creativity and independence, a bit of clutter is pretty much unavoidable. With that in mind, you want to make sure you’ve got plenty of space for storage to keep things as tidy and organised as possible, while ensuring they’ve also got space to play.

You don’t need to sacrifice comfort to be space-conscious, though, as luckily there are lots of fantastic space-saving alternatives to the standard kids’ single bed that still ensure a comfy night’s sleep.