Roman numerals
I, II, III, IV — counting like the Romans.
Where it came from
Romans used a base-10 system with letters: I, V, X, L, C, D, M. It served an empire for centuries without zero or place value. The modern "subtractive" shortcuts (IV for 4, IX for 9) were formalized in the Middle Ages.
They refuse to die: movie copyright years (MMXXIV), clock faces, book volume numbers, and Super Bowl titles all use them as a stylistic choice.
How it works
Values add left to right, but a smaller numeral before a larger subtracts (IX = 10−1). There are rules: never repeat V, L, D; subtract only I, X, C and only from the next two ranks.
Valid range is 1–3999 (no symbol for 5000+). UWC converts Roman ↔ Arabic both ways in your browser, rejecting malformed strings.
Convert Roman numerals
Turn MCMLXXXIV into 1984 (or back) — instantly, on your machine.