Mattress Firmness & Ergonomic Pillow Thickness Selector

Choosing mattress firmness by body weight and sleep position

The tool starts from a firmness score of 5.5 out of 10 and adjusts it for weight, sleep position and pain: −1.2 for side sleepers, +1.8 for stomach sleepers, +1.2 between 86 and 105 kg. The score is then turned into a firmness level, a mattress type and a pillow height.

Score calculation (1 to 10)

• Base: 5.5.
• Weight: −1 below 60 kg; +1.2 above 85 kg up to 105 kg; +2.2 above 105 kg; no change from 60 to 85 kg.
• Position: side −1.2; stomach +1.8; back +0.5; combination 0.
• Pain: lower back +0.8; neck and shoulders −0.4; widespread or none: 0.

The score is rounded to one decimal and capped between 1 and 10. Up to 3.5: plush; up to 4.8: medium-soft; up to 6.5: medium; up to 8.2: firm; above: extra firm. The pillow depends only on position: 11-14 cm for side sleepers, 9-11 cm on the back, 5-8 cm on the stomach.

Examples

72 kg, side sleeper, lower back pain (defaults): 5.5 − 1.2 + 0.8 = 5.1, medium. 95 kg on the stomach: 5.5 + 1.2 + 1.8 = 8.5, extra firm. For couples the tool compares both scores: from a 2.2-point gap it suggests a dual-firmness mattress or two joined mattresses. A 55 kg side sleeper (3.3) and a 90 kg back sleeper (7.2) are 3.9 points apart.

Limits

There is no official firmness standard: each manufacturer uses its own scale, and the same "7/10" does not feel the same across brands. The tool's coefficients are rules of thumb, not the result of a clinical study. Sleeping temperature only changes the suggested materials, not the score, and bed size plays no part. With persistent pain, trying a mattress in store and asking a doctor or physiotherapist remain the better route.

Frequently Asked Questions

What mattress firmness is best for side sleepers?

Side sleepers need their shoulders and hips to sink in a little: the tool takes 1.2 points off the 5.5 base score. For 72 kg with no pain this gives 4.3, a medium-soft mattress, with a thick 11-14 cm pillow.

Do I need a firm mattress for back pain?

Not necessarily a very firm one: the tool adds 0.8 points for lower back pain, which usually points to medium to firm rather than extra firm. No official standard defines ideal firmness; with persistent pain, ask a doctor or physiotherapist.

Which mattress should I choose if I weigh over 100 kg?

The tool adds 1.2 points between 86 and 105 kg and 2.2 points above 105 kg. A 110 kg back sleeper gets 5.5 + 2.2 + 0.5 = 8.2, a firm mattress with stronger support.

What if two sleepers have different needs?

The tool computes a score for each person. From a 2.2-point gap it suggests a dual-firmness mattress or two joined 80 or 90 cm mattresses; below that, one shared medium mattress is enough.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.