Choosing mattress firmness by sleeping position

Firmness labels aren't standard

Makers describe firmness in words ("medium firm") or numbers ("7/10"), but the National Bed Federation (NBF) points out that there is "no industry-wide standard to compare firmness ratings from one manufacturer to the other". One brand's medium can feel like another's firm.

On this site we copy each maker's own wording and place it on a simple five-step scale so you can filter by it:

SoftMakers call it soft or plush
Medium-softSoft-medium, medium-soft
MediumMedium, balanced
Medium-firmMedium-firm, medium/firm
FirmFirm, extra firm

Our 5-step scale simply maps each maker's own description. There's no industry standard, so two "medium-firm" mattresses can feel different.

What you're aiming for

The NBF says the right support depends on "your weight, height, build and even preferred sleeping position". A mattress should mould to your shape while keeping you supported: when you lie on your side your spine should be horizontal, and you should be able to turn over fairly easily.

The Sleep Charity puts it simply: a mattress that's too soft lets you slouch, while one that's too firm "can apply pressure to our hips and shoulders".

By sleeping position

Back sleepers — the NBF says back sleepers "may like a firmer feel than people who sleep on their sides". The hand test below is a useful check.
Side sleepers — put the other way round, side sleepers may like a slightly softer feel than back sleepers, so the shoulders and hips can sink in enough for the spine to stay level.
Front sleepers — neither the NBF nor The Sleep Charity gives front-sleeper-specific advice on the pages we checked, so use the general checks: your back shouldn't dip, and you should be able to turn easily.
If you move around a lot — choose something you can turn on without effort; the NBF lists being "able to turn fairly easily" as a sign of good support.

Body weight and couples

"As a general rule, the heavier you are, the firmer the tension you will need," says the NBF. If two partners differ in weight by 3 stone (18kg) or more, it suggests that different mattresses may be needed — some makers sell two singles that zip together, or one mattress with a different tension on each side.

Two quick tests in the shop

Lie down properly. Wear comfortable clothes, take off your coat and shoes, and lie on the mattress for at least 10 minutes in your usual sleeping position — on your side as well as your back.
The hand test. Lie on your back and slide a hand into the hollow of your back. If it slides in too easily, the mattress may be too hard; if it's a struggle, it's probably too soft. A little resistance may mean it's about right.

A bad back doesn't automatically mean a hard bed

The NBF says it used to be believed that a hard bed was good for a bad back, but "nowadays it's generally accepted that this is not necessarily the case". It also warns that "orthopaedic" is "a term loosely used by manufacturers to refer to extra firm models" — it does not mean a bed has been professionally assessed.

The NHS back pain page advises keeping active and not staying in bed for long periods, and explains when to get medical help.

Pillows matter too

The Sleep Charity says a good pillow keeps your head in the same line with your shoulders and spine as when you stand with good posture: too soft and your head flops; too hard and you may get a crick in the neck. The NBF suggests replacing pillows at least every two or three years.

Buying online

You can't lie on a mattress before you buy online, which is why many makers offer home trials. Trial lengths and conditions vary — check them before you order. See our guide to bed-in-a-box mattresses.