Web Tools
Roman Numeral Converter
Convert between decimal numbers and Roman numerals. Supports values 1-3999 with proper subtractive notation (IV, IX, XL, XC, CD, CM). Includes a quick reference table. Runs entirely in your browser — your data never leaves your machine.
roman numeral converter number decimal classic
Published May 30, 2026
All interactive tools run entirely in your browser. Your data never leaves your device.
How It Works
Enter a decimal number (1-3999) to convert it to a Roman numeral, or type a Roman numeral to get its decimal value. The converter uses standard subtractive notation (e.g., IV for 4, IX for 9).
Features
- Bidirectional: decimal to Roman or Roman to decimal
- Standard notation: proper subtractive pairs (IV, IX, XL, XC, CD, CM)
- Validation: strict Roman numeral validation (rejects invalid forms like IIII)
- Range: supports integers 1 through 3999
- Case-insensitive: accepts both upper and lowercase Roman numerals
- Quick reference: displays all 13 base Roman numeral values
- Roundtrip safe: convert to Roman and back yields the original number
- 5 examples: common conversions in both directions
- Private: runs entirely in the browser — no data transmitted
Use Cases
- Converting years or chapter numbers to Roman numerals
- Decoding Roman numerals found in books, clocks, or documents
- Educational tool for learning the Roman numeral system
- Quick reference for Super Bowl, Olympic, or papal numbering