A standard twin bed frame measures 39 inches wide by 75 inches long by 7.5 inches high. A twin extra-long frame measures 39 inches wide by 80 inches long by 7.5 inches high and is more suitable in length for a single adult.
Twin bed frames vary only slightly in length and width. On the other hand, the height varies considerably from one frame to another. Some antique bed frames are as high as 18.5 inches and require a stool to use comfortably. Other modern bed frames are higher than 7.5 inches to allow room for extra storage or a trundle bed.