What is the standard size of a futon mattress?

The standard full futon mattress size is 54 inches wide and 75 inches long. A twin futon and a queen futon have the same length, with widths of 39 inches and 60 inches, respectively. California King futons are 72 inches wide and 84 inches long, while the Eastern King futon is 76 inches wide and 80 inches long.