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. Here’s what our Head of Sleep Science recommends:

• 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? Expert Guidance.

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

Looking for unbeatable value? Our Sleep Experts suggest trying:

• 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

Our Sleep Experts suggest choosing 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

Why buy your king size mattress from MattressOnline?

We're mattress specialists, rated 4.7 out of 5 by more than 72,000 Trustpilot reviewers across the UK.

• Award-winning service: We're a six-time NBF Bed Retailer of the Year, so you can trust how we source, sell and deliver all of our mattresses, beds and bedding.
• Choice you can trust: Over 40 brands, from everyday value to handmade luxury, all in stock and ready to deliver.
• Expert advice: Our experts, led by our Head of Sleep Science, help you choose the right mattress for the way you sleep in partnership with leading UK sleep brands.
• Eco-first: Add old mattress recycling at checkout and we'll take your old one away and recycle it responsibly with our professional mattress recycling partners.

How much should you pay for a king size mattress?

Our Mattress Experts know that finding the correct mattress for your budget can be tricky, that’s why we’re here to help. 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 MattressOnline, 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.