The standard size for a twin bed is 39 inches wide by 75 inches long; for a double bed, 54 inches wide by 75 inches long and for a queen bed, 60 inches wide by 80 inches long. An extra-long twin measures 36 by 80 inches.
Mattresses range in depth depending on brand and model. At 80 inches long, the extra-long twin and the queen compare to the standard king mattress. The California king mattress is the longest at 84 inches. Both the standard and California king are wider than the queen at 76 and 72 inches respectively. The standard king is the widest bed found in stores.