Roman Numeral Converter
Convert between Roman numerals and Arabic numbers. Bidirectional conversion with validation. Includes reference table. Free online tool.
Why Use a Roman Numeral Converter?
Roman numerals are still used today in outlines, clock faces, movie sequels, monarch names, and formal documents. Converting between Roman and Arabic numerals can be error-prone when done manually, especially for larger numbers. Our converter handles the translation instantly in both directions, with built-in validation to catch invalid inputs.
Key Features
- Bidirectional conversion: Arabic → Roman and Roman → Arabic
- Input validation with clear error messages
- Reference table with all standard Roman numeral symbols
How to Use
- Select the conversion direction using the tabs
- Enter an Arabic number (1-3999) or a Roman numeral
- View the converted result and copy if needed
Technical Details
Arabic to Roman conversion uses the subtractive notation algorithm, processing values from largest to smallest (M=1000, CM=900, D=500, etc.). Roman to Arabic conversion scans left to right, adding values and handling subtractive pairs (IV=4, IX=9, etc.). The tool validates Roman numeral input by reconverting the result to ensure correctness. Range: 1-3999.
FAQ
Why is the maximum number 3999?
Standard Roman numerals don't have a symbol for 5000 and above. While extended notations exist using overlines, the standard form only supports 1-3999 (MMMCMXCIX).
What are the subtractive pairs?
The valid subtractive pairs are IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). Other combinations like IM or VX are not valid.
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