Roman Numeral Converter

Roman Numeral Converter translates in both directions: a number into Roman numerals, and a numeral back into a number.

The system uses seven letters: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. Values are normally written largest first and added together, so MMXXVI is 2,026. The complication is the subtractive rule: when a smaller value sits immediately before a larger one it is subtracted instead, which is why 4 is IV rather than IIII and 9 is IX rather than VIIII.

Only six subtractive pairs are valid in the standard system: IV, IX, XL, XC, CD and CM. A numeral like IL for 49 looks reasonable and is not correct; 49 is XLIX. The converter follows the standard rules when writing numerals, and when reading one it tells you if what you typed breaks them rather than guessing at an answer.

The range runs from 1 to 3,999. There is no zero in the system, no way to write a negative, and nothing above 3,999 without the overline notation that multiplies a letter by a thousand, which has no agreed plain-text form. Those limits are the system's, not the converter's.

Everything is worked out inside your browser. Nothing you enter is uploaded, logged or stored, which matters for the financial calculators in particular: the figures you put into them are nobody else's business.

• Converts in both directions
• Breakdown showing how the numeral was assembled
• Validates a numeral and explains what is wrong with an invalid one
• Reference chart of values and subtractive pairs
• Handles the full 1 to 3,999 range
• Explains why the range stops there
• Runs in your browser

The roman numeral converter is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Reading a date on a building, a book or a film credit
• Writing a chapter or appendix number
• Setting a clock face or an engraving
• History and maths homework
• Naming a sequel or an annual event