A UK king size mattress is 150 x 200cm, or 5ft x 6ft6. That's 15cm wider and 10cm longer than a double, so it's the size most families move to when a double starts to feel crowded, whether that's a couple, a tall teenager or a toddler who turns up at bedtime.
Our king size mattresses
- MemoryTeen 18: 18cm, memory foam, medium-firm. A king for a teenager's room.
- QuiltRest: 23cm, coil sprung, medium-firm.
- OrthoSupport: 23cm, coil sprung, firm.
- PocketBalance: 23cm, 1000 pocket springs, medium-firm.
- MemorySupport: 25cm, firm coil springs under memory foam.
- VitalRest: 25cm, pocket springs with foam layers, medium-firm.
- NaturalLoft: 28cm, 1500 pocket springs with wool, medium-firm.
- Copper Drift 1000 (medium), Copper Crest 2000 (firm), Copper Summit 3000 (medium) and Copper Zenith 4000 (medium-firm): our Copper hybrids, 25 to 27cm deep.
How big is a king size mattress compared with a double?
A king is 150 x 200cm; a double is 135 x 190cm. Shared by two, a king gives each person 75cm of width instead of 67.5cm, and the extra 10cm of length helps anyone over about six foot. A super king adds another 30cm of width. See double mattresses to compare.
Is a European king the same as a UK king?
No. A European king is 160 x 200cm, 10cm wider than a UK king. A UK king mattress will leave a gap in a European king frame, and a European one won't fit a UK frame. If your bed came from a European brand, measure the inside of the frame before you order.
Which king size mattress should I choose?
Start with how you both sleep. Side sleepers usually prefer a medium feel, such as the Copper Drift 1000. Back sleepers tend to like medium-firm, such as the PocketBalance or VitalRest. Front sleepers and anyone who likes to lie on top of the mattress should look at our firm mattresses. Pocket springs keep one person's movement on their own side, which helps if you go to bed at different times.
Will a king size mattress fit up my stairs?
Rolled mattresses are by far the easiest. Many of ours arrive rolled and vacuum-packed, so they go round tight landings in a box and open up in the bedroom. Each product page says how the mattress is delivered.
King size mattresses: common questions
What size bedding do I need?
King fitted sheets made for 150 x 200cm, with a pocket deeper than the mattress, and a king size duvet. Mattresses deeper than 25cm usually need deep-fitted sheets.
Is a king size mattress worth it for a teenager?
If the room has space, yes. A king gives a growing teenager room to stretch out, and the MemoryTeen 18 comes in king size. See our beds for teenagers.
Do you sell king size beds as well?
Yes, see our king size beds.
How long should a king size mattress last?
Usually several years, longer if you rotate it regularly. Our guide on how often to change a mattress lists the signs it's time for a new one.
Not sure which to choose? Message our family team with your bed's size and the maximum mattress depth on its product page, and we'll point you to the right mattress.
Written by the Millie & Jones family team. Last updated October 2026.
