Roman Numerals
Convert between decimal numbers and Roman numerals.
Free & unlimited
All processing happens in your browser. No data is sent to any server.
About this tool
- 1
Choose conversion direction
Select Arabic-to-Roman or Roman-to-Arabic conversion.
- 2
Enter a value
Type an Arabic number (1-3999) or a Roman numeral string.
- 3
View the result
See the converted value instantly with validation for correct Roman numeral formatting.
- Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500), M (1000).
- Subtractive notation: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900.
- Standard Roman numerals can represent values from 1 to 3999 (MMMCMXCIX).
- Roman numerals are still used for clock faces, book chapters, Super Bowl numbers, and movie sequels.
- Bidirectional conversion (Arabic to Roman and back)
- Input validation with error messages for invalid numerals
- Supports values from 1 to 3999
- Breakdown showing each symbol's contribution to the total
- Convert chapter or section numbers for formal documents.
- Decode Roman numerals on clock faces, monuments, and inscriptions.
- Generate Roman numeral labels for outlines and lists.
- Verify correctness of Roman numeral formatting.
Standard Roman numerals use M (1000) as the largest symbol, and no symbol can repeat more than three times. So MMMCMXCIX (3999) is the largest representable number without extended notation like vinculum (bar notation).
A bar over a Roman numeral multiplies its value by 1000. For example, V with a bar means 5000. This allows representation beyond 3999 but is rarely used today.
Both have historical use. IV (subtractive notation) is the modern standard, but IIII is still commonly seen on clock faces - a tradition possibly dating back to the 14th century.