Roman Numeral Converter
Convert between numbers and Roman numerals
About Roman Numeral Converter
Roman Numeral Converter works both ways as you type: a whole number from 1 to 3999 becomes its Roman numeral, and a numeral becomes its number. Lowercase letters are accepted and shown in capitals. Only the standard form is read, the one the converter itself writes, so IIII, IM, VX, or MMMM are flagged instead of being turned into 4, 999, 5, or 4000. Zero, decimals, exponents, and numbers above 3999 have no standard numeral and get a message, and the Copy Roman numeral button copies the numeral only.
Example
Four entries and what the page shows (the page's own conversion code, run in Node on October 6, 2026).
You type
Number: 2026 Number: 3999 Roman numeral: mcmxciv Roman numeral: IIII
The other field shows
MMXXVI MMMCMXCIX 1994 (the numeral is shown as MCMXCIV) nothing, and the message: "IIII" is not a valid Roman numeral (standard form, 1 to 3999 — for example 4 is IV, not IIII).
How to convert numbers to Roman numerals
- 1Type a whole number in "Number (1–3999)", or a numeral in "Roman numeral".
- 2The other field fills in as you type, and a red message explains any value that cannot convert.
- 3Click "Copy Roman numeral" to copy the numeral to your clipboard.
Formats and limits
- Range
- 1 to 3999, I to MMMCMXCIX
- Letters
- I, V, X, L, C, D, and M, in capitals or lowercase, in standard subtractive form only
- Refused with a message
- IIII, IM, VX, MMMM, and other non-standard numerals; 0, decimals such as 12.5, exponents such as 1e3, numbers above 3999
- Copy
- Copies the numeral only, not the number
Where your numbers are processed
Both directions are computed by this page in your browser, and nothing you type is sent. If copying to the clipboard fails, the page sends the fixed text Copy to the clipboard failed to our error log, with the tool's name and your browser's name and major version.
Frequently asked questions
Does it accept IIII for 4?
No. A numeral is accepted only if it is exactly the standard form the converter writes for that number, so 4 must be IV and 999 must be CMXCIX, not IM. The page says the numeral is not valid rather than guessing a value for it.
What is the largest number it converts?
3999, written MMMCMXCIX. In standard form no letter repeats more than three times, so MMMM for 4000 is refused, and zero and fractions have no standard numeral either; each of these gets a message instead of a result.
Can I type lowercase numerals?
Yes. mcmxciv is read as MCMXCIV and gives 1994, and the Roman numeral field switches your letters to capitals as you type, so you can copy the standard spelling straight away.