How to use it
Pick a direction
Choose Number → Roman or Roman → Number with the toggle.
Type your value
Enter a whole number from 1 to 3,999, or a Roman numeral like MCMXCIV. Lowercase works too.
Read the breakdown
The result updates instantly with a line showing how each symbol adds up. Copy it with one click.
Reference table
About the Roman numerals converter
Roman numerals build numbers from seven letters — I, V, X, L, C, D and M — adding symbols from largest to smallest and using subtractive pairs like IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). This converter applies those rules in both directions and validates input by converting the result back, so non-standard forms are caught rather than silently accepted. Lowercase input is fine: mcmxciv converts the same as MCMXCIV. It is handy for clock faces, movie and book copyright years, chapter and outline numbering, monarch and pope names, and Super Bowl titles.
Questions
Is anything uploaded?
No. The conversion runs entirely in your browser — nothing is sent to a server, stored or tracked.
Why does it stop at 3,999?
M (1,000) is the largest standard symbol and a symbol may repeat at most three times, so MMMCMXCIX — 3,999 — is the biggest number the classic seven-letter system can write. Larger numbers historically used a bar (vinculum) over a numeral to multiply it by 1,000, which is outside the standard notation this tool follows.
Why is IIII marked as invalid?
The converter follows standard subtractive notation, where 4 is written IV. It checks your numeral by converting the parsed value back and comparing, so non-standard forms like IIII or VIIII are flagged even though their letters sum to the right value. Clock faces, which traditionally use IIII, are the famous exception to the rule.