Why weight changes the answer
On your back, your weight is spread widely, but your hips and pelvis still carry a large share of it. The job of the mattress is to stop them sinking below the line of your shoulders. The heavier you are, the further the same materials compress, so the firmness needed to hold that line goes up.
In our scoring rules, the comfort window for a back sleeper under 130 lb is 4–7/10. At 230 lb and above it is 7–10/10. The chart above shows every step in between. A mattress that is perfect for a lighter partner can be noticeably too soft for a heavier one, even though it is the same mattress.
Support and durability are not the same thing
Support is how level you lie on the mattress as it is today. Durability is whether it will still hold you that way after a few years. Higher loads tend to compress comfort layers and foam cores faster, so a mattress can be supportive for a heavier sleeper now and lose that support sooner than it would for a lighter one.
That is why it is worth reading the support and durability scores together, and reading any watch-outs before the headline number. A strong overall score with a durability warning is still a durability warning.
How the engine handles heavier sleepers
A few rules change when you tell us you weigh 230 lb or more:
- Durability counts 1.5× its default weight and support 1.1×. As a back sleeper, support gets a further 1.15×; reporting lower-back discomfort adds 1.4× more.
- All-foam mattresses lose 1 point of durability, because foam cores tend to compress faster under higher sustained loads than coil cores.
- If a mattress’s independent durability rating is below 7/10, your results show a sag-risk watch-out with a suggestion to check the warranty’s sag terms.
The engine never raises that warning from an estimate. If no durability rating is on file, the dimension is marked Estimated instead, so you know the gap exists. See the full rules on How It Works.
What to check before you buy
- Find your comfort window for your weight, and look for a firmness near its center rather than at the soft edge.
- Prefer a supportive core: pocketed coils or a dense foam or latex base, rather than a thin core under thick soft layers.
- Read the warranty’s definition of a sag: the depth that counts as a defect, and how it must be measured. Our buying checklist explains what to look for.
- If you sit on the edge to get up, check edge support too; see edge support explained.
