A king size mattress measures 150 × 200cm: 15cm wider and 10cm longer than a double. That extra length is why a king suits anyone approaching six foot, and the extra width is what lets two people who sleep differently share one bed well. This guide explains how to choose the best mattress for a king size bed: the size to check, the differences between pocket sprung, memory foam and hybrid constructions, how firm to go, and what changes when a mattress gets this big.
King size, measured: 150 × 200cm
A UK king size mattress is 150 × 200cm, or 5ft by 6ft 6in. An EU king is 160 × 200cm and a US queen is 152 × 203cm. They are not interchangeable: a UK king mattress on an EU frame leaves a 10cm gap down one side. Measure the frame, not the label. Ours are the UK standard, matched exactly to our king frames, and every UK size is set out in the UK bed size guide.
What changes when you go up to a king
Width buys independence. Each sleeper gets 75cm, against 67.5cm on a double, so partners can differ in weight and firmness preference and both still be supported. The length buys the same thing for tall sleepers: 200cm means feet stay on the mattress.
What does not improve by itself is motion transfer. A wider surface carries movement further if the mattress is built as one continuous unit, which is why individually pocketed springs matter more as beds get bigger, not less. And weight: a king mattress is heavy, so the frame underneath has to be built to carry it, and rotating it is a two-person job worth doing every few months.
King size mattress types explained
The construction decides how a mattress feels, how warm it sleeps and how it handles two people. These are the four you will meet.
Pocket sprung. Hundreds or thousands of springs, each sewn into its own fabric pocket so it moves on its own. Support follows the shape of the body, movement on one side travels less to the other, and air moves through the spring unit, so it sleeps cooler than solid foam. The count (1,500, 2,500, 3,000) tells you how finely the surface responds; the comfort layers on top decide the feel. The construction most UK makers, including us, build on.
Memory foam. A dense foam that softens with body heat and moulds to the shoulders and hips. Excellent pressure relief and very little motion transfer, but all-foam mattresses hold warmth and can feel slow to move on. In a king, a solid foam slab is also the hardest type to turn.
Hybrid. A pocket spring unit with a substantial foam, gel-foam or pillow-top layer above it. The aim is spring support and airflow with foam-style cushioning. "Hybrid" is a loose label, so look at what sits on top of the springs: gel memory foam cools where plain memory foam warms, and a pillow top adds a cushioned first impression. Three of our four mattresses are hybrids in this sense.
Natural fillings. Pocket springs with wool or other natural fibres as the comfort layer instead of foam. Wool breathes and regulates temperature through the night, which makes it the choice for warm sleepers and anyone who wants a softer, more yielding surface without foam.
How firm should a king size mattress be?
Firmness is a feel, not a measure of support. Support comes from the spring unit; firmness is how the comfort layers above it receive you. The rule of thumb: heavier sleepers and back or front sleepers usually want medium-firm, so the hips do not sink below the shoulders; lighter sleepers and side sleepers usually want medium or medium-soft, so the shoulder and hip can settle in. On a king, the width means a couple with different preferences can each have their own 75cm without compromising the other, which is the practical reason to choose a king when you share a bed. If in doubt between two feels, take the slightly firmer one: a mattress topper can soften a bed, but nothing makes a soft mattress supportive.
Choosing by how you sleep
Side sleepers. The shoulder and hip need to sink enough to keep the spine level. Look for a generous comfort layer: memory foam, gel memory foam or a wool Euro top over pocket springs.
Back and front sleepers. The hips need holding up. Medium to medium-firm pocket sprung with a thinner comfort layer, ideally zoned so the middle third is firmer.
Couples who sleep differently. Choose on the heavier sleeper's support and the lighter sleeper's comfort, and prioritise individually pocketed springs so one person turning over stays on their side of the bed.
Warm sleepers. Avoid solid memory foam. Choose pocket springs with gel memory foam or natural wool above them, so warmth has somewhere to go.
Weight, bases and the frame underneath
A king mattress typically weighs 40 to 60kg depending on construction, so two people should handle it. It needs a base that supports it evenly across the full 150cm: a sprung-slat or solid-platform frame in the correct UK king size. Every bed we make is built to carry a king mattress, and our mattresses are made to the same 150 × 200cm standard as our frames, so there is no gap and no overhang. Our mattresses are designed to be rotated head to toe, not flipped.
King or super king?
A super king is 180 × 200cm, 30cm wider than a king, with the same length. Choose super king if two people share the bed and either moves a lot, if a child or dog joins in, or if the room is at least around 3.6m wide. Choose king if the room is tighter, if you want to walk comfortably round both sides, or if the extra width would not be used. Length is identical, so height is never the deciding factor between the two. Both sizes are in our king size beds and super king beds collections.
Choosing between ours
We make four mattresses, all in king size, all with a 60-night home trial and a five-year guarantee.
- Structured, medium to medium-firm support with cooling gel memory foam: the Arete 1500 pocket sprung gel memory foam mattress, 1,500 springs in seven zones, around 31cm deep. Our first suggestion for back and front sleepers, couples and warmer sleepers.
- Deeper memory-foam cushioning at medium-firm: the Laurel Comforto 2500, 2,500 springs with a visco memory foam layer and a fully encapsulated edge, 33cm deep. Suited to side and combination sleepers and to couples who want pressure relief with little partner movement.
- Natural wool and a softer welcome: the Laurel Natural 2500, 2,500 zoned springs under a natural wool comfort layer and a quilted satin Euro top, medium to medium-soft. The choice for warm sleepers and side sleepers who want a yielding surface without foam.
- The hotel pillow top: the Tranquility 3000 pillow top pocket sprung mattress, 3,000 zoned springs, cooling gel memory foam and a quilted pillow top, 33cm deep, medium to medium-firm.
Sleep on the decision rather than reading it: the 60 nights are there so the mattress can prove itself in your own room. Browse every mattress we make, or read the full method in how to choose a mattress.
A short checklist before you decide
- Measure the frame: 150 × 200cm is UK king.
- Decide support first (spring unit), then feel (comfort layer).
- Share the bed? Choose for the heavier sleeper's support and insist on pocket springs.
- Sleep warm? Gel foam or wool over springs, not solid memory foam.
- Check the depth against your base and your fitted sheets.
- Confirm the trial and guarantee in writing, and how the mattress is delivered to the room.
Questions people ask about king size mattresses
What size is a king size mattress?
150 × 200cm, or 5ft by 6ft 6in: the UK standard king.
Is a king mattress worth it over a double?
If the room takes it, yes. The 200cm length is the deciding gain for anyone tall, and the extra width is what lets two people sleep well together. The width is comfort; the length is necessity.
Do king mattresses need a special base?
A king frame in the UK standard size, with even support across the full width. Ours are matched exactly to our king mattresses and built to carry the weight.
How heavy is a king size mattress?
Typically 40 to 60kg. Treat moving and rotating it as a two-person job.
Which king size mattress is best for couples?
One with individually pocketed springs, so movement stays on one side, chosen for the heavier sleeper's support. If one of you sleeps warm, prefer gel foam or wool above the springs.
How long should a king size mattress last?
A well-made pocket sprung mattress that is rotated regularly should give seven to ten years of good support. Replace it when it no longer feels supportive after a night away, or when a dip stays after you get up.
What about the trial and warranty?
Every mattress we sell carries a 60-night home trial and a five-year guarantee.
Further reading: the best mattress for a double bed, where the trade-offs run the other way, and pocket springs, explained, on what 1,500 to 3,000 actually means.