Mattress Firmness Guide: How Firm Should Your Mattress Be?
Short answer: most people sleep best on something in the medium to medium-firm range. Go softer if you sleep on your side or weigh less; go firmer if you sleep on your stomach or back, or weigh more. The rest of this guide shows how to pick your number and how to fix a bed that turned out wrong.
Your starting point in 30 seconds
- How do you sleep most of the night? Side, back, stomach, or a mix.
- Roughly what do you weigh? Under about 130 lb, 130–230 lb, or over 230 lb.
- Find your row below, then aim for the middle of the range.
What the 1–10 firmness scale means
Brands describe feel in different ways, so many reviewers use a simple 1–10 scale: 1–3 is soft, 4 is medium-soft, 5 is medium, 6 is medium-firm, 7–8 is firm and 9–10 is extra firm. Medium-soft to medium-firm (about 4–6) is the most common range; most makers offer something there.
Firmness is how the bed feels when you lie on it. Support is different: it is whether the bed keeps your spine in a straight, neutral line. The top comfort layers mostly decide the feel; the core (coils or dense foam) mostly decides support. A soft bed can still be supportive, and a hard one can still let your hips sag if the core is worn.
Firmness by sleep position and body weight
| You mostly sleep on your… | Under ~130 lb | ~130–230 lb | Over ~230 lb |
|---|---|---|---|
| Side | 3–5 (soft to medium) | 4–5 (medium-soft to medium) | 6–7 (medium-firm to firm) |
| Back | 3–5 | 5–7 (medium to firm) | 7–9 (firm to extra firm) |
| Stomach | 4–6 | 5–7 | 7–9 |
| Combination | 3–5 | 4–6 | 7–8 |
Ranges follow the firmness guidance published by the Sleep Foundation (“Mattress Firmness: Finding the Best Firmness for You”, read October 16, 2026). They are starting points, not rules: personal preference matters.
Why position matters
- Side sleepers put their weight on the shoulder and hip. A bed that is too firm pushes those points up and bends the spine; a bed that is too soft lets the middle sag. Most side sleepers want enough cushion for the shoulder to sink in a little.
- Back sleepers need the bed to hold up the lower back and stop the hips from dipping. Medium to firm usually does that, with a little give for the natural curve of the spine.
- Stomach sleepers are the most likely to get an arched lower back on a soft bed, because the hips and belly sink. Firmer is usually better.
- Combination sleepers change position through the night, so a middle feel (about 5–6) and a surface that is easy to move on tend to work best.
Why weight matters
The same mattress feels softer to a heavier person and firmer to a lighter one, because more weight sinks further into the comfort layers. Height plays a part too: a tall person’s weight is spread over a bigger area, so the bed can feel a little firmer to them than to a shorter person of the same weight. If you and your partner land in different rows, look at mattresses sold with two different feels on each half, or pick the middle and adjust one side with a topper.
What about back pain?
A 2021 systematic review of 39 studies on mattresses, sleep quality and low back pain found that a medium-firm mattress promoted comfort, sleep quality and spinal alignment, compared with soft or extra-firm beds. In other words, “as hard as possible” is not the answer for most people with back pain. If you have a diagnosed back or joint condition, ask your doctor or physical therapist what they recommend for you.
Source: Caggiari G. et al., “What type of mattress should be chosen to avoid back pain and improve sleep quality? Review of the literature,” Journal of Orthopaedics and Traumatology, 2021 (abstract read October 16, 2026).
Signs your mattress is the wrong firmness
| If you notice… | It’s probably… |
|---|---|
| Numb arm, sore shoulder or hip in the morning (side sleepers) | Too firm |
| Lower back ache that eases once you’re up and moving | Too soft, or a sagging core |
| Feeling “stuck” or hot, hard to roll over | Too soft |
| A visible dip where you sleep | A worn mattress, not a firmness problem; a topper won’t fix it |
Already bought one? How to adjust it
- Too firm: give it a few weeks first: many new mattresses soften a little as the foams break in. If it is still too firm, a 2–3 inch soft topper adds cushion without replacing the bed.
- Too soft: a firm topper can help a little, but it can’t add support a sagging core has lost. Check that your base or slats are solid and evenly spaced, too.
- Use the trial: many mattresses bought online come with a home trial and return window. Check the length and any return fee before you buy, and keep the receipt.
Quick checklist before you buy
- Your position and weight row from the table above
- Your partner’s row, if you share the bed
- Do you sleep hot? Thick memory foam can feel warmer; coils and latex usually breathe more.
- Trial length, return fee and warranty terms
- A base that suits the mattress (solid or slatted, slat gaps as the maker specifies)
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Filter by firmness, size and type, and check each listing's trial and return terms.
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