<P> Iron beds appear in the 18th century; the advertisements declare them as free from the insects which sometimes infested wooden bedsteads . Elsewhere, there was also the closed bed with sliding or folding shutters, and in England--where beds were commonly quite simple in form--the four poster was the usual citizen's bed until the middle of the 19th century . </P> <P> Bed sizes vary considerably around the world, with most countries having their own standards and terminology . While the "double" size appears to be standard among English speaking countries, based on the imperial measurement of 4 ft 6 in by 6 ft 3 in (137 cm x 190 cm), the sizes for other bed types tend to vary . The mainland European sizes differ, not merely because of the use of the metric system . </P> <P> In the mid-1950s, the United States bedding industry introduced a new size: the king size . A king - sized bed differs from the other sizes in implementation, as it is not common to have a king - sized box spring; rather, two smaller box - springs are used under a king - sized mattress . It is a common misconception that in a US "standard" or "Eastern king", the box springs are identical in size to a "twin extra-long"; however, "twin extra-long" mattresses next to each other add up to 78 inches (200 cm) wide instead of the 76 inches (190 cm) width that is standard for an "eastern king". Another size variant in the United States is the "California king", which measures 72 by 84 inches (180 cm × 210 cm) long (narrower but longer than the standard king). </P> <P> What is referred to as a "single bed" in many parts of the world may also be known in US terminology as a "twin bed ." In some countries, a "twin bed" may also be used to describe one of two single beds in the same room . As another example, in some cultures, the "full mattress" is referred to as a "master size bed ." </P>

When did the king size bed come out