Roman Numeral Converter
Convert between Arabic numbers and Roman numerals instantly with our free bidirectional converter. Auto-detects whether your input is a number or Roman numeral and converts accordingly. Supports the standard range of 1 to 3999 using proper subtractive notation (IV, IX, XL, XC, CD, CM). Includes a reference table for quick lookup. Perfect for students learning Roman numerals, writers using them in outlines and chapter headings, clock enthusiasts, and anyone who encounters Roman numerals in daily life. Runs entirely in your browser with no data sent anywhere.
Reference Table
How to Use
- 1
Enter Input
Type an Arabic number (1-3999) or a Roman numeral (I-MMMCMXCIX) into the input field.
- 2
Auto-Convert
The tool auto-detects your input type and converts it to the opposite format instantly.
- 3
Copy Result
Click Copy to save the converted numeral for use in documents, outlines, or designs.
Examples by Niche
2024 → MMXXIV — perfect for copyright notices, book chapter numbering, and formal document headers.
IV → 4, IX → 9 — decode Roman numerals from clock faces, building cornerstones, and movie credits.
Practice converting numbers like 1999 → MCMXCIX to understand subtractive notation rules.
Frequently Asked Questions
What is the valid range for Roman numerals?
Standard Roman numerals represent numbers from 1 (I) to 3,999 (MMMCMXCIX). The system does not have a standard symbol for zero or for numbers above 3,999 without extended notation.
What is subtractive notation?
Subtractive notation places a smaller numeral before a larger one to indicate subtraction: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. This prevents awkward sequences like IIII or VIIII.
How does auto-detection work?
If your input contains only the letters I, V, X, L, C, D, and M (case-insensitive), it is treated as a Roman numeral and converted to a number. Otherwise, it is treated as an Arabic number and converted to Roman numerals.
Why do some clocks use IIII instead of IV for 4?
Many clock faces use IIII instead of the subtractive IV for aesthetic symmetry — it visually balances the VIII on the opposite side. This is called the "watchmaker's convention" and dates back to the 14th century. Both IIII and IV are historically valid, but this converter uses standard subtractive notation (IV).
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