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Roman Numeral Rules Cheat Sheet

Roman-Numerals.net · https://roman-numerals.net/printables/rules/

  1. Use only I, V, X, L, C, D, and M for the standard 1–3999 range.
  2. Write larger values before smaller ones when adding (XVI = 16).
  3. Use only the six subtractive pairs: IV, IX, XL, XC, CD, CM.
  4. Do not repeat V, L, or D. Do not repeat I, X, C, or M more than three times in a row in canonical form.
  5. Prefer canonical forms: 4 = IV, 9 = IX, 40 = XL, 90 = XC, 400 = CD, 900 = CM.
  6. This site’s converters reject non-standard strings such as IIII or IL and show the canonical form when possible.

Examples: 49 = XLIX · 944 = CMXLIV · 1999 = MCMXCIX · 2026 = MMXXVI