Convert 1–3999 to Roman numerals and back, with validity checking for invalid numerals like IIII.
Type either form, get the other.
Type a number like 2026 to get MMXXVI.
Or type Roman numerals like MCMXCIV to get 1994.
Direction is detected automatically from your input.
Invalid numerals are flagged with a clear message.
Built for speed, privacy and reliability — on any device.
Numbers become Roman numerals and Roman numerals become numbers — detected automatically.
Invalid numerals likeIIII are caught with a clear message, not silently converted.
Every number from 1 to 3999 — the complete standard Roman numeral range.
Conversion runs locally — nothing is sent anywhere.
No account, no limits.
Standard Roman numerals cover 1 (I) to 3999 (MMMCMXCIX) — beyond that requires special overline notation.
The converter validates structure: IIII is invalid (should be IV) and the result must match standard subtractive notation.
A smaller numeral before a larger one subtracts — IV is 4 and CM is 900. The converter reads and writes it correctly.
No. Conversion runs entirely in your browser.
The tool works in all modern browsers including Google Chrome, Mozilla Firefox, Microsoft Edge, Safari and Opera. We recommend keeping your browser up to date for the best experience.
Step-by-step guide with screenshots and tips.
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Read guide →Step-by-step guide with screenshots and tips.
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