About the Roman Numerals
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 the Roman Numerals
- Type an ordinary number between 1 and 3999 to get the Roman form.
- Or type a Roman numeral to convert it back to a number.
- Letters are case-insensitive, so mcmxcix works as well as MCMXCIX.
- Invalid sequences such as IIII or VX are flagged rather than silently accepted.
The formula behind it
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. A smaller value placed before a larger one is subtracted, which is how IX becomes 9.
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.