Young Blonde Girl Waking Up In The Bed

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 (137,16 cm x 190,5 cm), the sizes for other bed types tend to vary. The mainland European sizes differ, not merely because of difference based on use of the metric system.
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 on a U.S. 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 wide instead of the 76 inch width that is standard for an eastern king.
U.S. terminology refers to a twin bed to mean what is known as a single bed in other countries, whereas other countries understand twin beds to be two single beds in the same room.