The Quick Answer
80% of sleepers prefer a firmness between 5-7 on a 10-point scale. The most popular rating is 6 (medium-firm), which offers a good balance of comfort and support for most people. Once you know your ideal firmness, see our top-rated mattresses in Ireland.
Firmness vs Support: What's the Difference?
Many people confuse firmness with support, but they're different things:
Firmness
How soft or hard the mattress feels when you first lie down. This is the initial sensation – how much you sink in and how the surface conforms to your body.
Support
How well the mattress keeps your spine aligned throughout the night. A mattress can be soft yet supportive, or firm yet lacking proper support.
💡 Key insight: You need both the right firmness AND proper support. A mattress that feels comfortable but doesn't support your spine properly will lead to back pain over time.
The Mattress Firmness Scale Explained
Most mattress reviews use a 1-10 firmness scale. In practice, almost all mattresses fall between 3-9, as extremes are uncomfortable for most people.
| Rating | Feel | Description | Best Suited For |
|---|---|---|---|
| 1-2 | Extra Soft | Very deep sinkage, maximum conforming | Rarely recommended – insufficient support for most |
| 3 | Soft | Significant sinkage, close body hugging | Very lightweight side sleepers (<55kg) |
| 4 | Medium Soft | Noticeable sinkage, good pressure relief | Lightweight sleepers, side sleepers under 75kg |
| 5 | Medium | Balanced sinkage and support | Average weight side sleepers, lighter back sleepers |
| 6 | Medium Firm | Slight sinkage, moderate conforming | Most popular – suits majority of sleepers |
| 7 | Slightly Firm | Minimal sinkage, good support | Back/stomach sleepers, heavier side sleepers |
| 8 | Firm | Very little sinkage, strong support | Heavier sleepers (100kg+), stomach sleepers |
| 9-10 | Extra Firm | Almost no give, maximum support | Very heavy sleepers, specific medical needs |
Visual Firmness Scale
Firmness by Sleep Position
Your sleep position is the most important factor in choosing firmness — see our full guide to the best sleeping position for the pros and cons of each. Here's what experts recommend:
🛏️Side Sleeper
Side sleeping puts pressure on shoulders and hips. A softer mattress allows these areas to sink in, keeping the spine aligned.
🔙Back Sleeper
Back sleepers need lumbar support to prevent the lower back from sinking. A firmer surface maintains proper spinal curvature.
⬇️Stomach Sleeper
Stomach sleeping can strain the lower back. A firmer mattress prevents the pelvis from sinking too deep, reducing spinal stress.
🔄Combination Sleeper
Combination sleepers need versatility. A medium-firm mattress offers enough support and comfort across all positions.
How Body Weight Affects Firmness
The same mattress feels different depending on your weight. A 60kg person and a 100kg person will experience different levels of sinkage and support on identical mattresses.
Lightweight
Under 60kg (9.5 stone)Lighter sleepers don't compress mattress materials as much, so a softer mattress feels firmer to them. They typically need softer options (3-5) for adequate pressure relief.
Average Weight
60-100kg (9.5-15.5 stone)Most mattresses are designed for this weight range. Medium to medium firm (5-7) works well for most sleepers in this category.
Heavyweight
Over 100kg (15.5+ stone)Heavier sleepers compress materials more deeply and need firmer support (6-9) to maintain proper alignment and prevent bottoming out.
Signs Your Mattress Firmness is Wrong
Too Soft
- •Waking up with lower back pain
- •Feeling like you're sinking into a hammock
- •Difficulty changing positions during sleep
- •Hips sinking deeper than shoulders
- •Feeling unsupported or unstable
Too Firm
- •Pressure pain in shoulders or hips (side sleepers)
- •Numbness or tingling in arms/hands
- •Tossing and turning to get comfortable
- •Gaps between your body and the mattress
- •Waking up with stiff, achy joints
Special Considerations
Couples with Different Preferences
If partners prefer different firmness levels, consider:
- • Split firmness mattresses – different firmness on each side
- • Medium-firm compromise – works for most combinations
- • Mattress toppers – add softness to one side if needed
Back Pain Sufferers
Research shows medium-firm mattresses (5-7) are often best for back pain:
- • Provides support without creating pressure points
- • Maintains natural spinal curvature
- • Allows some conforming for comfort
- • Consult a physiotherapist for personalised advice