Movie credits (MCMXCIX), book chapters, clock faces, Super Bowls: Roman numerals persist two millennia after the empire. Converting them by hand is teachable in four rules.
Updated August 15, 2026, after a fresh review, with updated visuals and links.
The tool converts both directions between 1 and 3999; the guide below makes the system click permanently.
The four rules that cover everything
Added symbols sum: VII is 5+1+1 = 7, and XXX is 10+10+10 = 30. Reading left to right, bigger symbols first.
A smaller symbol before a bigger one subtracts: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, CM is 900. Only those six pairs work; IL for 49 is invalid.
A symbol never repeats more than three times: 4 is IV, not IIII (traditional clock faces break this rule with IIII, a historical quirk).
Standard form tops out at 3999 (MMMCMXCIX): Romans drew bars over letters for thousands, which digital text handles poorly, hence the tool's range.
Worth remembering
- Break long numerals into place values: 1987 is 1000 + 900 + 80 + 7 which reads M + CM + LXXX + VII = MCMLXXXVII.
- Movie copyright years are the classic excuse to practice: challenge yourself before checking with the tool.
Frequently asked
Why is 4 written IV and not IIII?
Subtractive notation (one before five subtracts) is the classical standard for inscriptions; IIII survives mostly on clock faces.
Is there a Roman numeral for zero?
No: the system has no zero, which is one reason arithmetic in it is painful and positional systems replaced it.
