King Size Mattresses

How big is a king size mattress?

Our king size mattresses measure 5' x 6'6" (150cm x 200cm) - ideal for taller sleepers, couples, or anyone wanting more room to stretch out in comfort.

How firm are king size mattresses?

Our king size mattresses come in a full range of firmness levels:

• Soft-medium - gentle cushioning
• Medium - balanced support for most sleepers
• Medium-firm - ideal for couples with different sleep styles
• Firm - great for back sleepers
• Extra firm - our most supportive feel

Need help deciding? Check out our mattress firmness guide for expert advice.

What king size mattress brand should I choose?

We offer king size mattresses from the UK’s most trusted brands, plus our own value ranges.

Looking for unbeatable value? Try:

• Komfi - long-lasting comfort at a great price
• Bodyshape - supportive and reliable comfort
• Luna - simple comfort with unbeatable value

Explore our mid-range king size mattresses from brands loved across the UK, and around the world:

• Silentnight - the UK’s number one mattress brand
• Sealy - posture-focused support backed by science
• Sleepeezee - Royal Warrant holders with 100+ years of heritage
• Millbrook - handcrafted with natural materials in Hampshire
• Emma - multi-award-winning memory foam technology
• Simba - hybrid innovation for restless sleepers
• Relyon - handcrafted British comfort since 1858

Choose from our premium king size mattresses built for ultimate indulgence:

• Hypnos - Royal Warrant holders with eco-conscious craftsmanship
• Harrison Spinks - 100% natural fillings and advanced pocket springs
• TEMPUR - NASA-recognised pressure relief for next-level comfort

How much should you pay for a king size mattress?

King size mattress prices vary by brand and the materials used, and we’ve got options for every budget:

• Budget: from £200 - cheap king size mattresses that deliver great value and everyday comfort
• Mid-range: £400-£600 - enhanced support and extra features for blissful sleep
• Premium: £600-£3,300+ - luxury comfort from leading brands with handcrafted quality

At Mattress Online, we’re committed to bringing you the best value at every price point – from cheap king size mattresses to premium models. Shop our latest king size mattress sale for even better deals.

Do your king size mattresses come with a warranty?

Yes, every king size mattress includes at least a 1-year warranty or guarantee, with many offering up to 10 years of coverage.

You can sleep easy, knowing you're protected for years to come.

Can I get a king size mattress with next day delivery?

Absolutely. Order your new king size mattress before 4pm for free next day delivery across most of the UK.

• Delivery 7 days a week
• Choose your preferred delivery date at checkout
• Handled by our expert local or national teams

See all delivery options.