The Roman numeral for the number four is IV. The Roman numeral system uses combinations of letters to form numerals. The basic letters in the system are I for one, V for five, X for 10, L for 50, C for 100, D for 500 and M for 1,000.
No more than three of the same letters can be used consecutively in a Roman numeral. Although the number three is expressed as III, the number four has to be expressed as IV. Putting the letter of lesser value to the left of a letter with greater value indicates subtraction, while putting letters of equal or lesser value to the right of a letter indicates addition.