About the Roman Numerals
Roman numerals use seven letters: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. Values are written from largest to smallest and added, except in six subtractive pairs where a smaller symbol comes first: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. So 1994 is M + CM + XC + IV = MCMXCIV, and 2026 is MMXXVI. The breakdown under each result shows these parts.
Standard form covers 1 to 3999 (MMMCMXCIX): there is no zero and no negative numbers, and larger values historically needed an overline meaning ×1000, which has no standard plain-text form. Validation follows the modern rules: I, X, C and M repeat at most three times; V, L and D never repeat and are never subtracted; I may only precede V and X, X only L and C, and C only D and M; and only a single symbol may be subtracted.
When a numeral breaks a rule, the tool says which one — IC is rejected because I can only be subtracted from V and X — and shows what the letters add up to with the correct spelling (XCIX for 99). Some forms you may meet on clock faces and old inscriptions, such as IIII for 4, are traditional but not standard; they are flagged so you can decide. Lower-case input is accepted.
How to use it
- Type a number from 1 to 3999 on the left to get its Roman numeral.
- Or type a Roman numeral on the right to get its value.
- Read the breakdown to see which symbols make up the value.
- If a numeral is invalid, follow the explanation and the suggested correct form.