Roman Numeral Converter

Roman numerals use seven letters: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Numbers are built by combining these letters from largest to smallest. MMXXV = 1000 + 1000 + 10 + 10 + 5 = 2025.

Subtractive notation handles four numbers near each base: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900). The smaller letter sits before the larger to mean 'subtract'. So IV = 5−1 = 4, not IIII (which appears on clock faces but is non-standard).

Standard form has rules: a letter can repeat at most three times in a row (III, XXX, CCC), and only I, X, C, M may repeat. V, L, and D never repeat (you write X, not VV). Subtraction only uses I before V/X, X before L/C, and C before D/M — never IL or IC.

The classical maximum is 3999 (MMMCMXCIX). For larger numbers Romans used a vinculum (overbar) to multiply by 1000 — Ⅴ̄ for 5000 — but this is rare in modern use and not supported here.

1944 → MCMXLIV. Build it: 1000 (M) + 900 (CM) + 40 (XL) + 4 (IV). The greedy algorithm walks through the value table from largest to smallest and emits letters until the remainder is zero.

MCMXCIV → 1994. Read left to right: M=1000, CM=900, XC=90, IV=4. Whenever a smaller letter sits before a larger, subtract it from the next.

Year stamps are the most common modern use. 2024 = MMXXIV, 2025 = MMXXV, 2030 = MMXXX, 2099 = MMXCIX. Movie credits and copyright dates love these.

Super Bowl numbering: Super Bowl LVIII = 58. The NFL switched to digit-only numbering for Super Bowl 50 specifically because L looks like a one-letter number that doesn't 'feel' big.

Movie and TV copyright dates: 'MMXXIV New Line Cinema'. Producers traditionally use Roman numerals to make outdated copyright dates less obvious to viewers.

Monarch and Pope succession: Elizabeth II, Charles III, Pope Francis (Latin Franciscus, no number — but Pope John Paul II is JOANNES PAVLVS II in inscriptions).

Sporting events: Super Bowls, Olympiads (XXXIII Olympiad = 2024 Paris), WrestleMania.

Outline structure: I, II, III for top-level sections, then A, B, C and 1, 2, 3 underneath in the classic Harvard outline format.

Clocks: most analog clocks use Roman numerals 1–12, but with IIII instead of IV for the 4 — a centuries-old convention that balances visual weight with the VIII opposite.

Book front matter: pages numbered i, ii, iii, iv, v before the main content begins at Arabic page 1.

Writing IIII for 4 — visually common on clocks but non-standard everywhere else. This tool rejects IIII as invalid.

Doubling V, L, or D: VV, LL, DD are never valid. Use X, C, M instead.

Long subtractive chains: IC for 99 looks intuitive but is wrong — 99 = XCIX (XC + IX). Subtraction only crosses one base step (I before V or X, X before L or C, C before D or M).

Zero: there's no Roman numeral for zero. Medieval scribes used 'N' (for nullus) when needed, but classical Roman counting starts at I.

Negative numbers and fractions: not supported in classical Roman numerals. Romans used a separate fractional system (uncia, quadrans) for fractions, never negatives.