Roman Numeral Converter
Convert decimal numbers to Roman numerals and back.
Type a decimal number (1-3999) or a Roman numeral. Conversion is two-way and validates round-trips so 'IIII' is rejected in favour of canonical 'IV'.
Supported range: 1 to 3,999
How to use it
Type a decimal
Any integer from 1 to 3999.
Or type a Roman numeral
Both fields are live; type in either.
Copy the result
Copy button next to each field.
What is it?
A Roman numeral converter translates between the modern Arabic numerals we calculate with and the classical Roman notation still used for clock faces, book chapters, monarch names and movie sequels. Roman uses M=1000, D=500, C=100, L=50, X=10, V=5, I=1 with subtractive notation (IV=4, IX=9, XL=40, XC=90, CD=400, CM=900) to keep strings short.
When to use it
Looking up a copyright year on an old film print, deciphering a chapter number in a fancy edition, building a Super Bowl logo, naming a sequel, or schoolwork.
Common mistakes
Writing 'IIII' instead of 'IV' (some clock faces use IIII for tradition, but it's non-canonical). Repeating I, X, C, M more than three times in a row (illegal in standard form). And expecting numbers above 3999 to convert - they don't in basic Roman notation.
FAQ
- Why 1 to 3999 only?
- Classical Roman numerals lack a notation for 4000+ without overlines (an overline multiplies by 1000). To keep the round-trip canonical we stick to the standard range.