Roman Numeral Converter

Roman numerals explained

Roman numerals use seven letters to represent values: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Placing a smaller value before a larger one subtracts it — so IV is 4 and IX is 9. This tool converts any integer from 1 to 3999 to its canonical Roman numeral form, and parses any Roman numeral string back to an integer. Non-canonical forms such as IIII are flagged as invalid because the standard representation would be IV.

Roman numerals appear in book chapters, clock faces, movie copyright years, and sporting event titles. Enter a number or a Roman numeral and the result appears immediately. Both uppercase and lowercase Roman numerals are accepted.

FAQ

Why does IIII fail? The standard subtractive notation requires IV for 4. IIII is sometimes seen on clock faces but is not considered canonical in the formal system this tool follows.

What is the largest number supported? 3999 (MMMCMXCIX). The standard Roman numeral system does not have a notation for 4000 and above without using an overline convention that is not universally supported.

Are lowercase letters accepted? Yes. Input is converted to uppercase before parsing, so xiv, XIV, and Xiv all produce the same result.