Roman Numeral Converter

Roman numerals refuse to die: film credits and Super Bowls, clock faces, book chapters and prefaces, monarchs and popes, building cornerstones, tattoo dates. Seven letters — I, V, X, L, C, D, M — combine by simple addition, with the subtractive twist (IV is 4, IX is 9, XL is 40, CM is 900) that makes reading them a small puzzle and writing them error-prone.

This converter goes both directions for the full standard range of 1 to 3999. Number to Roman applies the canonical subtractive rules, so 2026 becomes MMXXVI, never the sloppy MMXXVI variants. Roman to number is strict where it counts: the parser validates by round-trip, so malformed input like IIII, VX or IC is rejected with a clear message instead of being silently guessed at — which matters when you are decoding a date from a building or verifying an engraving before it is committed to metal or skin.

Why 3999? Standard Roman notation has no symbol beyond M (1000), and convention caps clean representation at MMMCMXCIX. Larger numbers historically used an overline (multiplying by 1000) that plain text cannot express — an FAQ covers it. For years, dates, chapters and everything Roman numerals are actually used for today, 1–3999 covers all of it, instantly, in your browser.