Roman Numeral Converter
Convert any whole number from 1 to 3999 into standard Roman numerals, or convert a Roman numeral back into a regular number — with instant validation.
How to Use the Roman Numeral Converter
- Choose "Number → Roman" to convert a regular number into Roman numerals, or "Roman → Number" for the reverse.
- Type your number (1–3999) or Roman numeral (e.g. MCMXCIV) into the box.
- The converted result appears instantly, with a clear warning if your input isn't valid.
- Click "Copy" to copy the result.
Why Use This Tool?
Why is the range limited to 1–3999?
Standard Roman numerals use combinations of I, V, X, L, C, D and M with subtractive notation (like IV for 4 or IX for 9). Without inventing non-standard symbols, the largest number cleanly representable this way is 3999 (MMMCMXCIX) — beyond that, historical Roman numeral systems used special notation (like a bar over a numeral to multiply by 1000) that isn't part of everyday standard usage, so this tool sticks to the widely recognized 1–3999 range.
How does the conversion work?
Number → Roman repeatedly subtracts the largest matching value (from a table including subtractive pairs like CM=900, CD=400, XC=90, XL=40, IX=9, IV=4) and appends the matching symbol, working from largest to smallest. Roman → Number reads the numeral left to right, adding each symbol's value, but subtracting instead of adding whenever a smaller-value symbol appears directly before a larger one (like IV or IX).
What if I type an invalid Roman numeral?
The tool validates your input against real Roman numeral rules — for example it rejects numerals with too many repeated symbols (like IIII) or in the wrong order, and shows a clear message rather than an incorrect number.
Where are Roman numerals still used today?
You'll still see Roman numerals on clock faces, in movie and book copyright years, for naming monarchs and popes (like Elizabeth II), numbering Super Bowl games, and in outline/chapter numbering for formal documents.