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Roman Numeral Converter

Convert between Arabic numbers and Roman numerals. Free, no signup, works in your browser.

Result will appear here…

All conversion happens in your browser. No data is sent to any server.

About Roman Numeral Converter

This Roman numeral converter translates between standard Arabic numbers (1, 2, 3…) and Roman numerals (I, II, III…). Enter any number from 1 to 3,999 to see its Roman numeral form, or type a Roman numeral to get the decimal value. The converter validates input in both directions — it will catch invalid Roman numeral sequences like IIII (should be IV) and suggest the correct form. Useful for historical dates, clock faces, movie sequels, Super Bowl numbers, and outlines.

Frequently Asked Questions

What is the largest Roman numeral this tool supports?
The standard Roman numeral system goes up to 3,999 (MMMCMXCIX). Numbers above 3,999 require the vinculum (overline notation), which is not part of the standard system.
How do subtractive Roman numerals work?
When a smaller numeral appears before a larger one, it's subtracted. For example, IV = 4 (5 − 1), IX = 9 (10 − 1), XL = 40 (50 − 10), XC = 90 (100 − 10), CD = 400 (500 − 100), CM = 900 (1000 − 100).
Does this validate Roman numeral correctness?
Yes. The converter round-trips the conversion to verify correctness. If you enter a non-standard form like IIII, it will tell you the correct form is IV. Invalid characters and malformed sequences are flagged immediately.

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