King Size Mattress Dimensions UK: CM, Feet and Room Space

A standard UK king size mattress measures 150 cm wide by 200 cm long, which is approximately 5 ft wide by 6 ft 6 in long. These measurements refer to the mattress itself rather than the complete bed frame, which will usually have a larger overall footprint depending on its design.

If you are choosing a king bed, it is worth looking beyond mattress size alone. The width of the side rails, headboard, foot end and storage features can all affect how much bedroom space the finished bed requires. This guide explains the standard king mattress dimensions, how they compare with nearby UK sizes and what to measure before ordering. For a wider comparison, see our UK bed size guide.

What Are the Dimensions of a UK King Size Mattress?

A standard UK king size mattress measures 150 cm wide by 200 cm long. In imperial measurements, this is approximately 5 ft wide by 6 ft 6 in long.

The familiar term 5 ft king refers mainly to the mattress width. The 200 cm length also gives a UK king an extra 10 cm compared with a standard double mattress, which measures 190 cm long.

Are All King Mattresses Exactly 150 × 200 cm?

150 × 200 cm is the standard nominal UK king size, but small manufacturing tolerances can occur. The National Bed Federation notes that there is no legal UK mattress size tolerance and that accepted industry practice allows a small variation in stated length and width.

For most buyers, the important point is to treat 150 × 200 cm as the standard king mattress size and then check the dimensions supplied for the exact mattress and bed frame before ordering.

King Size Mattress vs King Size Bed Frame Dimensions

A 150 × 200 cm measurement refers to the mattress itself. The complete king size bed frame will usually be larger because the side rails, headboard, foot end and overall construction add to the external width and length.

There is no single overall measurement for every king bed frame. A slim metal frame may add relatively little bulk around the mattress, while a substantial wooden or upholstered design can take up noticeably more floor space.

The style of the frame also affects how large the bed feels within the room. Light timber, slim metalwork and softer neutral fabrics can give a king bed a lighter visual presence, while deeper side rails, bold upholstery and taller headboards can make the same mattress size feel more substantial.

When planning your bedroom, always use the external dimensions of the exact bed frame rather than assuming that a king bed will measure 150 × 200 cm overall.

How Much Room Does a King Size Bed Need?

There is no single bedroom size that automatically makes a king bed suitable. The best approach is to start with the external dimensions of the exact bed frame, then check how much usable space remains around it.

Allow enough room for normal movement around the bed, as well as opening bedroom doors, wardrobes and drawers. If you are considering an ottoman or storage bed, check that there is enough space to operate the storage comfortably without nearby furniture getting in the way.

Bedside tables also affect the overall layout. A king bed may fit between two walls, but once bedside furniture, lamps and circulation space are added, the room can feel much tighter than the mattress dimensions alone suggest.

Visual proportion matters too. A slim metal frame or lighter timber design can feel less dominant, while deep upholstery, darker finishes and tall headboards can give the same 150 × 200 cm mattress a much stronger presence. Colour, texture and frame depth therefore influence how balanced the room feels, even when the physical mattress size stays the same.

For more guidance on proportion and layout, see our guide to king bed frames and bedroom balance.

King vs Double vs Super King Mattress Sizes

A UK king mattress sits between a standard double and a super king. It gives you more width and length than a double without taking up as much room as a super king.

A UK king is therefore 15 cm wider and 10 cm longer than a standard double, while a super king keeps the same 200 cm length but adds another 30 cm of width.

If you are deciding between a double and a king, the extra width can make a noticeable difference to the overall sleeping area, but the larger frame footprint also needs to work comfortably with the room layout. For more detail on the smaller size, see our double mattress dimensions guide.

Will a King Mattress Fit an Existing Bed Frame?

A UK king mattress should be paired with a bed frame designed to take a 150 × 200 cm mattress. If you are replacing an existing mattress, measure the internal mattress area of the frame rather than relying only on the size name.

Check the usable width and length where the mattress sits, ideally without bedding in place. This is particularly important with older frames, imported beds or frames where the original specifications are no longer available.

Do not use the full external dimensions of the bed to judge mattress fit. The headboard, side rails and foot end all add to the overall footprint without changing the mattress area itself.

UK King vs European King

A UK king mattress measures 150 × 200 cm, while a European king sold by UK retailers is commonly 160 × 200 cm. That extra 10 cm of width means the two sizes are not normally interchangeable.

International bed-size names can vary between retailers and countries, so always check the measurements in centimetres before buying a replacement mattress or frame. The dimensions are more reliable than the label alone.

What Should You Measure Before Ordering a King Bed?

Before ordering a king bed, measure more than the 150 × 200 cm mattress area. The full frame can extend beyond the mattress, so use the external dimensions of the exact design when planning the room.

• Mattress size: confirm that the frame is designed for a 150 × 200 cm UK king mattress.
• Overall frame dimensions: check the full width and length, including the headboard and foot end.
• Room layout: allow for walking space, bedside furniture, wardrobes and door openings.
• Storage access: if the bed has drawers or ottoman storage, make sure there is enough space to use them comfortably.
• Delivery access: consider doorways, staircases, corners and landings, particularly with larger bed components.

A useful way to judge the scale is to mark the full external bed dimensions on the floor with masking tape. This gives a clearer impression of how the bed will sit alongside existing furniture than measuring the mattress footprint alone.

King Size Mattress FAQs

Is a 5 ft bed a king size in the UK?

Yes. In the UK, a 5 ft bed normally refers to a king size bed designed for a mattress measuring approximately 150 × 200 cm. The 5 ft description refers to the nominal mattress width.

Is a UK king mattress the same size as a US king?

No. A standard UK king mattress measures 150 × 200 cm, while a standard US king is approximately 193 × 203 cm. A US king is therefore considerably wider, so the two sizes should not be treated as interchangeable.

Are all king size mattresses the same depth?

No. King size refers to the mattress width and length, not its thickness. Mattress depth varies according to the construction and model, which can affect the finished bed height, fitted-sheet depth and how much of the headboard remains visible.