Roman Numerals

Rules of the system

1. Symbols write largest to smallest, left to right. Add them. VII = 5 + 1 + 1 = 7.
2. A smaller symbol before a bigger one means subtract. IV = 5 − 1 = 4, IX = 10 − 1 = 9.
3. Only I, X, C can be used as subtractive prefixes, and only before specific letters: I before V or X; X before L or C; C before D or M.
4. No symbol repeats more than 3 times in a row. So 4 is IV, not IIII. And 9 is IX, not VIIII.
5. V, L, D never repeat.

Common examples