The seven numbers on a mattress spec sheet, and what to do if they are missing

Most mattress pages are adjectives: luxurious, supportive, breathable, premium. None of those is a spec. A mattress is decided by seven numbers, and a maker who knows them will give them in a sentence. Here they are, with the ranges that mean something.

1. Depth, and what it is made of

The total height, and the height of each layer. Depth alone is meaningless; a 27 cm mattress could be 8 cm of comfort layers over springs or a cheap foam block. Look for the layer list. See how deep a mattress should be.

2. Spring count, stated for a king

Pocket springs are counted for a 5ft king by trade convention; a double has about 20 per cent fewer, a single about half. 1,000 is a full-size unit; 2,000 uses smaller springs; counts above that usually include a micro-spring layer and should be split out. Open coil counts are in the hundreds and not comparable. See 1,000 vs 2,000 springs.

3. Wire gauge

The thickness of the spring wire in millimetres. 1.8 mm is a typical medium; 2.0 mm and above is firm and more durable; under 1.6 mm in a main unit is a cost-cut. Rarely printed; always worth asking.

4. Spring height and edge

A main unit of 13 to 15 cm has proper travel. What holds the edge: a steel rod, or a foam rail and its density (30 kg/m³ adequate, 50 good). See steel edge or foam rail.

5. Foam density, per layer

Kilograms per cubic metre, for every foam layer. Memory foam: under 50 takes a body impression in a few years, 55 to 65 lasts, 70 and up is premium and warm. Support foam (CMHR): 40 to 45 is the good range. Base (reflex): 33 to 40. This is the number that predicts lifespan and the one most often missing. See memory foam density explained.

6. Hardness

Separate from density: how much force it takes to compress the foam, in newtons (or ILD). Low hardness at good density is a plush foam that lasts; low hardness at low density is a cheap soft foam that does not. Ask for both.

7. Cover and fire barrier

What the cover is made of (knitted polyester, Tencel, cotton, damask), whether it is quilted and to what, and what the fire barrier is: treated fabric, woven barrier, or fibreglass. See BS 7177 explained and fibreglass in mattresses.

The ones that are words, not numbers, but still matter

• Tension: is there a choice (Medium, Firm), and what changes between them?
• Zoning: is the spring unit zoned, and how?
• One-sided or two-sided: can it be flipped, or only rotated?
• Made in: which country, and ideally which factory. "Designed in the UK" is not "made in".
• Guarantee: how many years, what counts as a defect (usually a dip over a stated depth), and what voids it (usually the base).
• Delivery: rolled or flat, one person or two, to the door or the room.

If the numbers are missing

Ask, in writing, in one message: "Please give the depth of each layer, the spring count for a king, wire gauge, edge method, foam density and hardness per layer, cover fibre and fire barrier." A maker answers in a paragraph. A reseller who does not know will say "premium" again. Silence is an answer too: assume the lowest value in each range.

A worked example

Here is one of ours, read the way this guide suggests. The Single Life: 25 cm; 1,000 three-zone pocket springs (king), 1.8 mm wire, 14 cm high, foam-encapsulated in a 35 kg/m³ rail; 3 cm gel memory foam at 55 kg/m³ over 4 cm CMHR at 45 kg/m³ over a 33 kg/m³ reflex base; knitted stretch cover, lightly quilted, woven fire barrier, BS 7177 low hazard; Medium or Firm tension; one-sided, rotate; made in Yorkshire; ten-year guarantee; delivered flat by two people. Every chapter page reads the same way.

The short version

• Depth by layer, spring count for a king, wire gauge, spring height and edge, density per layer, hardness, cover and fire barrier.
• Then tension, zoning, sides, made in, guarantee, delivery.
• Ask for all of them in one message. The answer, or the lack of one, tells you what you are buying.