There is no industry standard for mattress firmness. A “medium” from Saatva and a “medium” from Nectar are not the same thing. This causes more buyer regret than almost any other issue in mattress purchasing — and it’s entirely preventable if you know what to look for.
The 1–10 scale is made up
Most brands rate firmness on a 1–10 scale, with 1 being softest and 10 being firmest. Sounds helpful. The problem: each brand calibrates this scale to their own product line. A 6 from one brand might feel like a 4 from another. Worse, body weight dramatically affects perceived firmness — a 150-lb person and a 250-lb person will experience the same mattress at different points on the firmness spectrum.
What matters more than the number: the materials. The ILD (Indentation Load Deflection) rating of the comfort layer is an actual measurement. An ILD of 14–19 is soft, 20–25 is medium, 26–31 is medium-firm, 32+ is firm. Brands that publish this data are being honest about what they’re selling.
How body weight changes everything
Weight and firmness — practical guide
- Under 130 lbs: Go one step softer than you think you need. Lighter sleepers don’t compress comfort layers enough to reach the intended feel — a “medium” often sleeps firm.
- 130–200 lbs: Most firmness ratings are calibrated for this range. The label is reasonably accurate.
- 200–250 lbs: Go one step firmer than you think. Heavier sleepers compress foam faster, which means softer mattresses bottom out sooner.
- 250+ lbs: Prioritize hybrids with reinforced coils and thicker comfort layers. Most consumer foam mattresses aren’t built for this weight range long-term.
Firmness by sleep position
Sleep position creates predictable pressure points. Side sleepers put maximum pressure on the shoulder and hip — they need a softer comfort layer to accommodate this without creating pain. Back sleepers need lumbar support without excessive sink — medium to medium-firm. Stomach sleepers need their hips to stay elevated so the spine doesn’t hyperextend — firm.
Combination sleepers — people who move between positions — need a mattress that works adequately in multiple positions. This usually means medium, with a responsive material (hybrid or latex) that adapts quickly rather than holding you in place.
The practical takeaway
Don’t buy a firmness rating. Buy based on your weight and primary sleep position, then use the trial period to verify. If you’re a side sleeper above 200 lbs who ordered a medium, and it’s sleeping too firm at night 30, you have time to exchange. Use it. The brands that make exchanges easy (Helix is particularly good at this) earn that reputation for a reason.