Roman Numeral Converter
Convert numbers to Roman numerals and back, in both directions at once — with strict classical validation of subtractive notation.
Validation follows the classical subtractive rules: I before V/X, X before L/C, C before D/M — so VIIII is rejected and IX is accepted.
This tool runs entirely in your browser. Your data never leaves your device — it is not uploaded to any server.
How to use
- 1Enter a number between 1 and 3999 to get its Roman numeral.
- 2Or type a Roman numeral — the number appears instantly.
- 3Invalid forms like VIIII or IM are flagged with an explanation of the rules.
Roman Numeral Converter
Type an Arabic number (1–3999) and see its Roman form, or type a numeral and get the number — both fields are live, so you can correct either side. The parser enforces classical rules: I before V/X, X before L/C, C before D/M.
Handy for clock faces, book chapters, film years, monument inscriptions and Super Bowl numbers — anywhere Roman numerals still appear.
Frequently asked questions
Why is 4000 the upper limit (MMMCMXCIX)?
Classical Roman notation has no digit larger than M (1000), and repeating M four times (MMMM) was not used. The largest number expressible in strict classical form is 3999, written MMMCMXCIX.
Why is VIIII rejected when clocks sometimes show it?
Some clock faces use additive IIII for four, but the standard classical system requires subtractive IV. This tool validates against the strict canonical regex, so VIIII, IC or IM are flagged rather than silently converted.
Does the converter accept lowercase letters?
Yes — input like mcmxciv is uppercased automatically and converted to 1994. The output is always shown in uppercase, as inscriptions traditionally are.
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Put this tool on your own site with one line — it runs entirely in the visitor's browser.
<iframe src="https://zoyku.com/en/tools/roman-numeral?embed=1" width="100%" height="640" style="border:0;border-radius:16px" title="Zoyku — roman-numeral" loading="lazy"></iframe>