The dimensions of a twin-size bed are about 38 inches wide by 75 inches long, according to the Better Sleep Council. About.com puts the dimensions at 39 inches wide by 75 inches long.
Twin-size mattresses may be too short for some men, points out the Better Sleep Council. Twin extra-long mattresses provide a few more inches in length and are popular in colleges.
About.com says that one advantage of twin beds is that their sheets cost the least of all sizes and come in many patterns. Sheets for twin extra-long beds are more difficult to find, however, and their patterns are limited.