🏛️ Roman Numeral Converter
2026 = MMXXVI. Type in either box and the other updates — with proper validation, so "IIII" and "IC" are flagged with their canonical spellings instead of silently accepted.
2026 = MMXXVI
Standard (subtractive) notation: I=1, V=5, X=10, L=50, C=100, D=500, M=1000; IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Malformed numerals like "IIII" or "IC" are rejected with the canonical spelling suggested. Converts locally.
How the roman numeral converter works
Number to numeral uses the standard subtractive notation: work down through M (1000), CM (900), D (500), CD (400), C, XC, L, XL, X, IX, V, IV, I, appending symbols greedily — 2026 becomes MM + XX + VI. Numeral to number reads left to right, subtracting a symbol when a larger one follows it (IX = 9) and adding otherwise — then the tool re-encodes the result and compares: if your input wasn't the canonical spelling ("IIII", "VX", "IC"), it's rejected with the correct form suggested, rather than silently interpreted. Standard notation covers 1–3999.
The validation is the differentiator: most converters happily accept "IIII" or even nonsense like "IC" (99 is XCIX — subtractive pairs only allow I before V/X, X before L/C, C before D/M). Strictness matters when you're checking an inscription, a movie copyright year (MCMXCIX = 1999), or a Super Bowl number. Above 3999 the Romans used an overline (vinculum) multiplying by 1000 — outside standard notation, so this tool stops at 3999 and says so.
Frequently asked questions
What are the Roman numeral symbols?
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. A smaller symbol before a larger one subtracts, in six allowed pairs only: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.
Why is 1999 MCMXCIX and not MIM?
Subtractive pairs are restricted: I may precede only V and X, X only L and C, C only D and M. So 1999 = M + CM + XC + IX. "MIM" breaks the rule, and this converter will tell you so.
What's the largest standard Roman numeral?
MMMCMXCIX = 3999. Larger numbers historically used a vinculum (overline meaning ×1000) — a different notation beyond the standard system this tool implements.
Why does it reject numerals other converters accept?
It re-encodes your input's value and requires the spellings to match — the definition of well-formed. Loose inputs like IIII (clock faces aside) get the canonical form suggested rather than a silent guess.
Does it work offline?
Yes — conversion is pure local logic.