Roman Numeral Converter

Roman numerals survive on clock faces, film copyright dates, book chapters, and Super Bowl branding. The system uses seven letters and a subtractive rule that makes IV four rather than six. This converter handles both directions and rejects malformed numerals rather than guessing at them.

How to use it

1. Type an ordinary number between 1 and 3999 to get the Roman form.
2. Or type a Roman numeral to convert it back to a number.
3. Letters are case-insensitive, so mcmxcix works as well as MCMXCIX.
4. Invalid sequences such as IIII or VX are flagged rather than silently accepted.

Frequently asked questions

Why does the system stop at 3999?

Because 4000 would need four M characters, which the standard notation does not allow. Larger numbers historically used an overline to multiply a numeral by a thousand, a convention that does not survive in plain text.

Is there a Roman numeral for zero?

No. The system has no symbol for zero and no concept of place value, which is a large part of why it was eventually displaced by Arabic numerals for calculation.

Which subtractive pairs are valid?

Only six: IV, IX, XL, XC, CD, and CM. Combinations such as IL for 49 are not valid; 49 is written XLIX.

How do I read a long numeral like MCMLXXXIV?

Break it into groups: M = 1000, CM = 900, LXXX = 80, IV = 4, giving 1984. Reading left to right in chunks is far easier than character by character.

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