Twin mattresses in the United States are generally 39 inches wide and 75 inches long. Mattress sheets usually say what size bed they fit on the packaging.
39" x 75" Be aware, sheets made in China are often off-size, and if you have a pillowtop mattress you really need to buy a full sheet to fit correctly.
The standard size for a twin mattress is 39 x 75 inches or 99 x 190 centimeters. This is the size you will find of most standard twin mattresses. There are also extra long twin mattresses. An extra long twin size is 39 x 80 inches or 99 x 203 centimeters.
