A full-size bed, also known as a double bed, is 54 inches wide and 75 inches long. A full-size mattresses has the same proportions. Thickness and firmness vary depending on the model and manufacturer.
In North America, beds and mattresses generally come in five sizes: twin, full or double, queen, standard king and California king. Twin beds measure 39 inches wide and 75 inches long, while queen beds measure 60 inches wide and 80 inches long. A standard king measures 72 inches wide and 80 inches long, which is 4 inches wider and 4 inches shorter than a California king.