How Big Is a King Size Bed?
The King of Mattresses

Last updated on March 22, 2019

In the United States, a standard king-size mattress measures 76" wide by 80" long. Compared to a standard queen-size bed, a king size mattress is the same length but 16" bigger in width.

Those who have king-size beds typically swear by them for the additional space they provide. If you or your partner take up a lot of sleeping surface or are easily disturbed, a king mattress may give you both the room you need. It can also come in handy if you have kids or pets that like to jump into bed with you.

The size can also be a drawback, though. It requires a more substantial and supportive foundation, larger and more expensive bedding and sheets, and you'll even want king-size pillows, as standard ones appear dwarfed.

The cost of a king mattress typically runs 20-30% higher than an equivalent queen-size bed (about $300 more, on average).

A king size mattress is almost exactly the same size as two twin XL beds, so if you like the size of a king, but you and your partner have different preferences, you could opt for two twin XL beds side by side, covered with king-size bedding.

King-Size Mattress Dimensions

Almost all king-size mattresses sold in the United States are the standard 76" x 80" size. Here are a few other variations.

California king mattresses -- occasionally referred to as "Western King" or "King Long" -- are actually 4 inches narrower than a standard King (making them 72" wide) but are also 4 inches longer (making them 84" long).  Although this size was first found primarily for hard-sided waterbeds, it has recently become one of the more popular sizes for any kind of bed due to its suitability for taller sleepers.  Many mattresses models are available in both standard and California king sizes.

7-foot square king beds are 8 inches wider than a standard king (84" wide) and 4 inches longer (84" long).  This size has been offered by at least two high-end mattress makers -- Aireloom / Kluft (billed as the "Aireloom King") and McRoskey (billed as the "San Francisco King").  The perfectly square shape of this mattress provides the added advantage of being able to rotate it periodically with quarter turns to ensure more even wear over time. Special sheets are required.

Grand king beds, first introduced by Sleep Number / Select Comfort, are 4 inches wider (80" wide) and 18 inches longer (98" long -- over 8 feet!) than a standard king, offering a sleep surface large enough for even the tallest people.

King split mattress models are roughly equivalent in size to two side-by-side twin XL mattresses (each 38-39" wide and 80" long).  Typically used with an adjustable base, having a split king mattress allows for each partner to raise and lower their head and foot independently of the other.  The king split construction also makes it easier to carry the mattress through a house with tight corners, doorways or stairwells.  In fact, the king split designation sometimes refers only to the foundation (aka, box spring), which due to its lack of flexibility can be difficult to relocate when tight spaces are involved.

How Big Is a King Size Bed in Canada?

Standard mattresses sizes in Canada are the same as in the United States, with a standard king measuring 76" x 80" or 193 cm x 202 cm. You can also find California king mattresses in Canada, but they are not nearly as popular, and may be harder to find; that would measure 183 cm x 213 cm.

Mattress sizes in the United Kingdom are quite different, however. A king size mattress in the UK measures 150 cm x 200 cm, or about 60" x 79", roughly the same size as an American or Canadian queen-size bed. A UK "superking" size is larger, measuring 180 cm by 200 cm, just slightly smaller than a US / Canadian king.

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