Convert numbers to Roman numerals (and back) with full step-by-step breakdown. Supports bidirectional conversion, year mode for dates, batch conversion, and extended range up to 3,999,999 using vinculum notation.
Switch between Number → Roman (convert a decimal number to Roman numerals) and Roman → Number (decode a Roman numeral string to its decimal value). Year mode lets you quickly convert years for tattoos, anniversaries, film credits, and formal documents.
For Number to Roman: type any integer from 1 to 3,999,999. For Roman to Number: type a valid Roman numeral string (I, V, X, L, C, D, M). Invalid symbols and combinations are highlighted with an error message explaining the rule that was violated.
The result shows the full Roman numeral (or decimal), plus a step-by-step table listing each Roman symbol (or number group), its value, and how it combines to form the total. The subtraction pairs (IV, IX, XL, XC, CD, CM) are highlighted and explained.
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. These seven symbols, combined according to specific rules, represent any integer from 1 to 3,999 in the classical system. For numbers over 3,999, extended notation uses a vinculum (overline) over a numeral to multiply its value by 1,000: V̄ = 5,000, X̄ = 10,000, M̄ = 1,000,000.
When a smaller value symbol appears immediately before a larger value symbol, it is subtracted. Only six subtractive pairs are valid: IV = 4 (not IIII), IX = 9 (not VIIII), XL = 40 (not XXXX), XC = 90 (not LXXXX), CD = 400 (not CCCC), CM = 900 (not DCCCC). These are the only valid subtractive combinations — mixing others (like IC for 99, which should be XCIX) is non-standard and considered incorrect.
The subtractive notation (IV for 4, IX for 9, etc.) was codified in medieval times to reduce the length and visual complexity of numerals. However, IIII was historically common — it is still used on many traditional clock faces (typically showing IIII for 4 rather than IV, supposedly for visual symmetry with the VIII on the opposite side). This converter uses standard modern notation (IV, IX, etc.) as taught in schools and used in academic and formal contexts.
Year mode is specifically designed for converting calendar years to and from Roman numerals. Common uses: copyright dates in film and television credits (© MMXXIV), tattoo design dates for birth years and anniversaries, formal invitations, chapter headings, and official event commemorations. The converter pre-fills the current year and shows the result instantly, making it easy to look up specific years.
Classical Roman numerals have no standard representation beyond 3,999 (MMMCMXCIX). Extended notation uses a vinculum (overline line) above a numeral to indicate multiplication by 1,000: V̄ = 5,000, X̄ = 10,000, L̄ = 50,000, C̄ = 100,000, D̄ = 500,000, M̄ = 1,000,000. This tool supports up to 3,999,999 using vinculum notation for the millions range.
Yes — no numeral may appear more than three times in a row. I, X, C, and M can each appear up to three consecutive times (III = 3, XXX = 30, CCC = 300, MMM = 3000). V, L, and D may never repeat (so 10 is X, not VV; 1000 is M, not DD). Violating these rules produces invalid Roman numerals. This tool validates your input and highlights any rule violations.
