How to measure mattress depth

There are many reasons why you may need to measure your mattress depth and thickness - whether you're buying new fitted sheets, your bed frame requires a mattress or a certain depth, or you just like a deeper mattress! 

In this guide, we’ll walk you through how to measure your mattress to get the correct depth.

What does mattress depth mean when measuring a mattress or bed?

There are many different ways to describe mattress depth, you might have also heard it referred to as: 

  • Mattress thickness 
  • Mattress height
  • Mattress loft

All of these terms describe the measurement taken from the base of the mattress to the very top of the mattress. Here at Mattress Online, we use the term ‘mattress depth’.

A close up of the side of the SleepSoul Cloud 800 Pocket Memory Pillow Top Mattress.
To ensure you are measuring your mattress depth correctly, please follow our instructions below

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How to measure mattress depth

Now we’re clear on what mattress depth is, it’s time to start measuring your mattress! For this you will need: 

  • A tape measure
  • Something long and flat that will stay on top of your mattress while you measure - like a metre stick or broom handle

Step 1

Remove all pillows, bedding and sheets from your mattress. You may be tempted to keep the sheets on, but it is important that you also take them off because tight sheets can disturb the fillings in your mattress, which can make it slightly taller.

Step 2

Make sure that your mattress is on a flat surface so that you can measure from the very bottom of the mattress. 

If the sides of your bed frame obscure the base of your mattress or you don’t have access to the bottom of your mattress because it sits ‘within’ the bed frame, you will need to take it out and measure it on the floor.

If your mattress is already resting on a flat divan base, great! You don’t need to move your mattress for this step.

Step 3

Place your chosen object on top of your mattress. This can be something like a:

  • Metre stick
  • Broom handle
  • Walking stick
  • Roll of cardboard

The aim is to have this long, flat item resting from the centre of your mattress to the edge.

Make sure that the metre stick (or item of choice) rests horizontally across the top of your mattress. If you crouch down next to your mattress so that you’re at eye level with the end of your mattress, you should be able to see that the middle of your mattress rises slightly higher than the rest of the surface. This is where you should place your object of choice.

This item should stay stationary while you conduct the next step.

Step 4

Time to measure!

Use your tape measure to measure from the very bottom of your mattress to where your metre stick (or object of your choice) rests.

This will give you the correct thickness of your mattress. 

Now you know how to measure your mattress depth correctly!

Top tip!

It can be very tempting to measure the depth or thickness from the top and bottom seams on the corner of your mattress - however, this does not give you the true depth of your mattress.

This method does not account for the extra lift that the surface of your mattress may have - especially if your mattress is tufted or has a pillow top.

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How to measure pillow top depth

Pillow top mattresses, also known as box-top or euro-top mattresses, have an additional layer that sits on the mattress surface for extra comfort and support. This makes the mattress deeper, but measuring thickness is exactly the same:

  1. Place your mattress on the floor. 
  2. Lay a metre stick or broomstick horizontally across the centre of the mattress. 
  3. Measure from the base of the mattress to the object on your mattress.

It’s that easy!

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Why you may need to know your mattress thickness

When looking for a new mattress, it's important to be aware of the mattress's thickness or depth. This is because some bed frames may have a recommended depth for safety reasons, such as bunk beds or adjustable beds. Or, some mattresses may require you to buy extra deep bed sheets due to their depth.

Bed sheets

When you buy new bed sheets or bedding sets, they often have a maximum mattress depth that they can fit.

If the sheets are too tight and put too much pressure on your mattress, it can disrupt the fillings and change the shape of your mattress. This can make your mattress feel more uncomfortable and cause the sides of your mattress to become misshapen.

If you’re looking for new fitted sheets, why not browse our options below? We have options for standard mattress depth and an extra deep option:

Mattress toppers and mattress protectors

Most mattress toppers and protectors have elasticated bands that you hook over the corners of your mattress. Because of this, you should find out the maximum depth of mattress they will comfortably fit.

If the mattress protector or topper is too tight, you could potentially damage it by stretching it out too far.

A person putting the Protect A Bed Cotton Mattress Protector over a mattress.
Like the Protect A Bed Cotton Mattress Protector, most toppers and protectors have a mattress depth limit.

Bunk beds

It is extremely important to make sure that your mattress depth is correctly measured when you buy a bunk bed

This is because the safety barrier for the top bunk needs to sit at around 16cm taller than the mattress - although this measurement can vary between manufacturers. If your mattress is too tall for the barrier, this can be a safety issue for your child as it increases the risk of them falling out of bed.

For more information on buying a bunk bed and the safety requirements around them, our bunk bed buying guide has everything you need to know.

A Casper Wooden Bunk Bed in a child's room
The Casper Wooden Bunk Bed requires a top bunk mattress that is 16cm thick.

Adjustable beds

Many adjustable beds have a maximum mattress height or depth limit. If your mattress is too tall for the height requirements, it could impact how smoothly the bed’s mechanisms run.

Also, adjustable beds are designed to help with your mobility and having a mattress that is too tall could affect your ability to easily get in and out of bed.

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Our thickest mattresses

If you’re looking for an extra thick mattress, check out the thickest mattresses we have to offer below:

The Silentnight Deluxe Box Top Mirapocket 2000 Limited Edition Mattress in a white bedroom.

Silentnight Deluxe Box Top Mirapocket 2000 Limited Edition Mattress

  • From only £474.95
  • Mattress depth: 39cm
  • Mattress type: Box top and Mirapocket
The Harrison Spinks Cotterdale 13250 Pocket Pillow Top Mattress in a barn-converted hotel room.

Harrison Spinks Cotterdale 13250 Pocket Pillow Top Mattress

  • From only £1464.45
  • Mattress depth: 37cm
  • Mattress type: Natural fillings
The Sleepeezee Jessica 2200 Pocket Plush Mattress in a luxury hotel room.

Sleepeezee Jessica 2200 Pocket Plush Mattress

  • From only £699
  • Mattress depth: 33cm
  • Mattress type: Pocket sprung

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Our thinnest mattresses

On the flip side, we’ve also collected our three thinnest mattresses for you:

The Bodyshape Value Memory Mattress in a pale pink bedroom

Bodyshape Value Memory Mattress

  • From only £156.62
  • Mattress depth: 16cm
  • Mattress type: Memory foam
The Emma One - close up on the mattress corner

Emma One Foam Mattress

  • From only £259.95
  • Mattress depth: 18cm
  • Mattress type: Memory foam
Luna Memory 1000 Pocket Mattress

Luna Memory 1000 Pocket Mattress

  • From only £199.95
  • Mattress depth: 20cm
  • Mattress type: Memory foam

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FAQs about mattress depths

Below we’ve included some of the most frequently asked questions about mattress depth and thickness. If you have any questions that aren’t included in this list, our Customer Service Team are more than happy to answer any questions you may have!

How thick is the average mattress?

Our average mattress thickness, also known as mattress depth, is around 25cm deep.

We have mattresses ranging from 16cm to 39cm deep, so no matter what mattress depth you need, we'll have the one for you. All of our mattress depths are listed in the product descriptions.

How thick should a mattress be?

There is no ‘correct’ thickness for mattresses as this entirely depends on personal preference unless you have a bed frame that requires specific measurements. 

For example:

  • Some bed frames are designed so that the mattress sits just inside the frame, which can affect how deep your mattress needs to be.
  • If you have a bunk bed, the mattress should be slimmer for health and safety reasons so that the safety barrier can protect your child.
  • Adjustable beds have a mattress depth limit to ensure that the lifting mechanisms work smoothly.

If you have any questions about your mattress depth, please don’t hesitate to get in touch! Our customer service team will be more than happy to help with any queries you may have.

Is it better to have a thicker mattress?

Thickness or mattress depth is not an indicator of whether a mattress is ‘better’ or ‘worse’ than another model - it entirely depends on your preference. 

Thicker mattresses tend to be on the more expensive side. They are usually made from natural materials such as wool and cotton. However, some thick mattresses are made from multiple layers of memory foam or gel foam.

Thinner mattresses tend to be more budget-friendly, but that doesn’t mean that they don’t provide high quality! Rolled mattresses such as Simba and Emma are quite thin but provide excellent comfort and support!

All you need to do is find out which type of mattress is best for you and we guarantee we will have a mattress with the depth you prefer.

How thick is a mattress?

There is no standard mattress height or depth. Every mattress has a different thickness, but the average mattress depth here at Mattress Online is 25cm.


We hope this guide has helped you in finding out your mattress depth and why it's so important when purchasing a new mattress.

If you’d like more information on the different mattress dimensions, our ‘Bed & Mattress Size Guide’ explains how you can find out which mattress size is best for you and we provide a list of all mattress sizes and dimensions.

Or, if you’d prefer to start browsing, our mattress category has everything you need.