How To Choose The Right Degree Of Firmness

How To Choose The Right Degree Of Firmness - UK Guide | 2025

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Written by Nicky Peters

Editor & Certified Sleep Therapist

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Last updated: 16.11.2024 Reading time: 8 Min.

Nicky

Nicky Peters

Editor & Certified Sleep Therapist

Nicky is an experienced writer and editor with numerous qualifications. As a certified sleep coach, her interests lie in understanding how sleep problems arise from hormonal and environmental issues, particularly as part of stress and anxiety management.

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You may know that you like your mattress as soft and fluffy as a cloud ... or as firm and stable as a table.

But what exactly does this mean and how can you translate these vague descriptions into a universally comprehensible firmness scale?

That's exactly what we'll be looking at in this article, walking you through what mattress firmness relates to and how firmness scales are created.

There's lots to cover, so let's get to it. 👇

Firmness Scales

What is a firmness scale?

The firmness of a mattress describes - as the name suggests - how soft or firm a mattress feels.

Differences in mattress firmness are caused by the use of different materials and their respective densities.

There are different types of mattress firmness:

What are soft mattresses?

These are generally memory foam mattresses with lots of body-contouring support, cushioning, and extra padding.

Soft mattresses are popular with people looking for superior comfort and relaxation and give you that sleeping-on-a-cloud feeling.

You'll often find mattresses that have an upper comfort layer of memory foam to provide extra squishiness.

What are medium-firm mattresses?

These are the perfect in-between, mattresses that are not too soft and not too firm.

Medium-firm mattresses will suit most people.

We could describe these as your marshmallow mattresses: still soft and squishy, but with a lot more firmness than a cloud.

What are firm mattresses?

Firm mattresses generally offer high levels of support and durability.

They are well-suited to athletes and people struggling with back pain and tension.

These are your sleeping-on-a-table mattresses, but, of course, there are also various levels here and not all tables are hard as concrete.

Unfortunately, there is no uniform industry standard for a mattress's firmness rating.

Some brands use terms like H2, H3, and H4, others simply describe their mattresses as soft or firm, and others, again, come up with their own firmness scale.

different degrees of firmness

This is also why we at Sleep Hero have created our own firmness scale, which helps us classify mattresses better.

We use our firmness scale in all our mattress reviews and buying guides to help you figure out which is the perfect mattress for you.

Why is the right degree of firmness so important?

Choosing the right degree of firmness is important for healthy spinal alignment. 📏

  • If your chosen mattress is too firm, your body will be forced to remain unnaturally straight, resulting in a misalignment of the spinal column.
  • On the flip side, if your mattress is too soft, you'll sink into the mattress too deeply, resulting in a hollow back.

In both cases, your spine will be misaligned, which can lead to tension and lower back pain.

If you choose the right mattress with the right degree of firmness, though, your body will sink in at the centres of gravity (i.e. your shoulder and pelvis) but remain well-supported everywhere else.

This allows your spine to remain straight throughout the night, easing tension and allowing for a comfortable night's rest.

What should a good mattress do?

A good mattress should relieve pressure and support the body.

It has to cushion the entire body, while still providing enough support. The shoulders and pelvis need to sink in more deeply so that the spine remains well-balanced.

walter braun sleep expert
Walter Braun [1]

Sleep Expert

If you already struggle with severe back, neck, or joint pain, it's even more important to be aware of firmness levels and choose a mattress with the right level of support.

What's the difference between mattress firmness and stability?

Even though we refer to firmness as "the factor that determines how well you're supported", there is a deeper aspect that you need to pay attention to, and it's important to note the difference between firmness and stability.

People often assume that a firm mattress is necessary to keep your spine straight and that a soft mattress will automatically lead to back pain.

This isn't necessarily true.

  • A firm mattress can result in back pain if it's not the right fit for you.
  • Similarly, a soft mattress can have excellent stability and be perfect for you.

You always need to choose a mattress with good stability, while firmness can be a matter of personal preference.

But your build, weight, and height will impact which degree of firmness is best for you to ensure that the mattress you choose can support your body.

How to find the right degree of firmness

Even if you have a mattress that offers good overall support and stability, you still need to find a mattress with the right degree of firmness for you.

finding the right degree of firmness

General sleeping preferences and your sleeping style may play a role, but the most important factors to consider include your weight, height, and preferred sleeping position.

You should consider the following general guidelines when choosing the right degree of firmness:

  • The heavier or larger you are, the firmer your mattress should be.
  • Side sleepers and lighter-weight people often require softer mattresses than back and stomach sleepers.
  • Conversely, back and stomach sleepers require firmer mattresses.
  • Your height also plays a role, and very tall people may require a firmer mattress.

Let's walk you through different ways of finding the right degree of firmness. 👇

Choosing the right degree of firmness according to body weight

Body weight is a decisive factor when selecting the right degree of firmness. 🏋️‍♀️

But, since you also need to consider height, build, and prefered sleeping position, we can only give general guidelines and you still need to consider everything on a case-by-case basis.

The following table may help you decide which degree of firmness is right for you:

Feeling Recommended body weight
H1 Soft Up to 60 kg (132 lbs)
H2 Soft to medium-firm 60 - 80 kg (132 - 176 lbs)
H3 Medium-firm 80 - 100 kg (176 - 220 lbs)
H4 Firm From 100 kg (220 lbs)
H5 Extra-firm From 130 kg (286 lbs)

Choosing the right degree of firmness according to sleeping position

Your sleeping position also greatly impacts which degree of firmness will be right for you.

  • Side sleepers: With side sleepers, only a few parts of the body touch the mattress. This means that your entire body weight is focused at these points, putting an enormous amount of pressure on the mattress and creating distinct pressure points. This is why side sleepers should choose slightly softer mattresses. These allow your hips and shoulders to sink into the mattress much more deeply, keeping the spine in a healthy alignment.
  • Back sleepers: Back sleepers generally do well on medium-firm mattresses. They need enough firmness to keep the spine in an optimal alignment, but they'll also require some give to allow the heavier pelvis to sink in.
  • Stomach sleepers: Stomach sleepers can afford to choose slightly firmer mattresses. They need more support to keep their hips lifted and prevent the formation of a hollow back.

It's worth remembering that sleeping position and body weight often work together in deciding which degree of firmness will be best for you.

Choosing the right degree of firmness for couples

Couples should pay special attention to the degree of firmness before buying a mattress.

This is simply because not every degree of firmness will be equally suitable for both partners. 👩‍❤️‍👨

In general, we'd recommend sticking to medium-firm mattresses and making use of risk-free trial periods to make sure both partners sleep comfortably.

If you and your partner are of largely varying heights or body weights, though, you may need to make a different plan:

  • Two single mattresses: One option would be to buy two single mattresses that are the same height but have different degrees of firmness. In this way, each mattress will be perfect for each individual, ensuring that both partners can sleep well. You can always buy a bed bridge to get rid of the little gap between the two mattresses.
  • Customisable mattresses: You could also invest in a customisable mattress. These are mattresses that offer different degrees of firmness on each side of the mattress so that each half can be individually adjusted. This is ideal but can be a little more expensive.

Zip-and-link mattresses are also an excellent option.

Choosing the right degree of firmness for children

Firmness is also important to consider when buying a mattress for your child.

While teenagers and children over the age of 6 can sleep quite comfortably on adult mattresses, babies, toddlers, and small children under 6 generally require a special cot mattress.

These offer the perfect medium-firm feel to support growth and healthy bone development.

If a child's mattress is too soft or too firm, there is a risk of spinal deformities developing - especially at an early age.

The Simba Hybrid Cot mattress is one of our favourites.

It's always worth spending a bit more time finding which degree of firmness works best.

Luckily, most bed-in-a-box brands offer risk-free trial periods, so you can always send a mattress back if it doesn't work for you.

The Sleep Hero firmness scale

If you've already browsed through our best mattress reviews, you'll undoubtedly have come across references to the Sleep Hero firmness scale.

We've decided to create our own firmness classification system as it allows us to more easily compare mattresses to each other.

We rate mattresses on a scale of 1 to 10, where 1 is the softest and 10 the firmest.

Our firmness scale is based on our personal experiences and comparisons with different people in different sleeping positions.

General feel Recommendation
Firmness 1 - 4 Very soft Side sleepers or very light-weight people
Firmness 5 - 7 Medium-firm Good for most sleeping positions & body weights
Firmness 8 - 10 Very firm Good for stomach and back sleepers & heavier-weight sleepers

Using our scale helps us recommend different degrees of firmness to people with different sleeping positions.

Some of our favourite mattresses:

Can you change your mattress's firmness level?

There is only one way to change your mattress firmness level, and that's by adding a mattress topper.

Mattress toppers are generally intended to soften up a firm mattress.

The thicker the mattress topper, the more of a noticable difference you'll feel.

It's worth noting that quilts, covers, and mattress protectors generally don't affect overall firmness, but they do safeguard your mattress against dirt, spills, stains, and bacteria.

If your mattress is too soft or not supportive enough, you'll need to buy a new mattress.

This is why we like risk-free trial periods, as they give you the chance to try the new mattress and send it back if it doesn't work for you.

Check out our favourite mattress toppers:

Understanding mattress firmness

Finding the right degree of firmness is essential, not only to the quality of your sleep but also to your health.

You need to find a mattress that will support you and keep your spine in an optimal alignment so you can wake up feeling refreshed and without any sort of tensions, aches, or lower back pain.

Our Sleep Hero firmness scale has been specifically designed to help you navigate the world of mattress firmness and find the mattress that's perfect for you.

Table of Contents

Frequently asked questions

  • What are contour zones?

    Some mattresses consist of contour zones, which typically appear in the base layer of the mattress and influence its overall support and stability.

    These are usually divided into the following zones:

    • Hips (pelvic area): This is the heaviest part of the body and the mattress must be able to provide sufficient support. But, it must also be soft enough so that the pelvic area can sink into the foams sufficiently if the sleeper lies on his or her side, enabling the spine to remain in a straight alignment.

    • Lower back (lordosis area): The mattress will need to be able to provide additional firmness and support in this area to prevent the formation of a hollow back.

    • Shoulders: This is another centre of gravity for the body. The mattress must provide enough support but allow for enough sinkage in the shoulder area.

    • Head and feet: The head and feet are comparatively light parts of the body and should, therefore, lie on a relatively soft zone.

    A typical zoned mattress will consist of 3, 5, 7, or even 9 contour or comfort zones.

  • Which mattresses are best for your back?

    A mattress that's good for your back will offer a high degree of stability, body-contouring support, and pressure relief.

    We can highly recommend memory foam mattresses, which are often designed with orthopaedic support.

    Many people will also benefit from a mattress with contour zones.

    Contour zones make it easier for your body to sink into the foams more deeply where required and be better supported where required. 

    A side sleeper, for example, will need to sink in more deeply in the shoulder and hip areas and require more support elsewhere.

    You may also want to read our guide on the best mattresses for back pain and the best orthopaedic mattresses.

  • Which degree of firmness should I choose if I struggle with herniated discs?

    If you suffer from a herniated disc [2], then choosing a mattress with the right support is of enormous importance.

    It's important to immediately relieve pressure and ensure that the spine always remains in a healthy alignment.

    In order to achieve this, your mattress of choice shouldn’t be too firm or too soft.

    For most people, soft or medium-firm mattresses in the H2 or H3 range should be good.

    However, it may also be helpful to discuss this with your orthopaedist, who will be able to give you valuable tips. 

  • I’m overweight; which degree of firmness should I choose?

    Anyone who weighs more than 100 kg (220 lbs) needs to pay special attention to the right degree of firmness.

    The incorrect firmness can lead to severe back, neck, and spine problems.

    We would recommend buying a firm mattress, generally in the 8 - 10 or H4 - H5 range.

    Heavier people will also do better on pocket sprung mattresses, as these offer better adaptability and pressure relief. 

    Pocket sprung mattresses also have the added advantage of allowing for good airflow, which is great for heavy sweaters.

  • Does mattress size impact mattress firmness?

    No, the size of your mattress will not have an effect on the firmness of your mattress.

    You can choose your desired mattress with your preferred level of firmness in a number of different UK mattress sizes.

    The standard UK mattress sizes include:

    Singles can generally choose any mattress size, while couples should opt for double mattresses or larger ones.

  • References

Nicky

Nicky Peters

Editor & Certified Sleep Therapist

Nicky is an experienced writer and editor with numerous qualifications. As a certified sleep coach, her interests lie in understanding how sleep problems arise from hormonal and environmental issues, particularly as part of stress and anxiety management.

Get to know the rest of our team

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