Nothing says "luxury" like a king-sized bed.
The largest of the traditional mattress sizes, the Standard King is the same length as a queen mattress, but is 16 inches wider. It’s the most expensive mattress and bedding size, but many find the extra room well worth the additional cost.
Pros: Width and comfort. 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.
Cons: Expense and size. As the most expensive of the four major mattress sizes, the biggest downside to a king mattress set is the price. The cost of a king mattress typically runs 20-30% higher than an equivalent queen-size model (~$300 more, on average). King-sized beds also take up a lot of space, and not every bedroom can comfortably accommodate a bed this large. In addition, linens that fit king mattresses are also the most expensive, and buying king-sized pillows is advisable.
Standard King beds -- sometimes known as "Eastern King" -- are 76” wide x 80” long. These dimensions are almost exactly the same size as two twin mattresses placed side by side. As a result, some king beds actually use two twin extra long box springs instead of a single king-sized foundation.
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. Today, many higher-end mattress models are available in the California King size, although they are still most prevalent in urban areas and in the western US.
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.
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 extra long 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.