Convert Roman Numerals to Decimal Online
Roman numerals appear in clock faces, movie copyright dates, chapter headings, sports event numbering (Super Bowl LVIII), and formal documents. Converting them to decimal numbers is straightforward with knowledge of the symbol values, but longer Roman numerals with subtractive notation (like IV for 4 or XC for 90) can trip up manual conversion. This tool converts any standard Roman numeral string to its decimal equivalent instantly. It handles the full range from I (1) to MMMCMXCIX (3999) including all subtractive notation forms. The converter validates the input and shows an error for non-standard or invalid Roman numeral strings, helping you identify typos or non-standard forms.
Enter a number (1-3999) to get Roman numerals, or Roman numerals to get the decimal value.
Decimal
Roman Numeral
FAQ
- What are the Roman numeral symbols and their values?
- I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Subtractive combinations: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.
- What is subtractive notation in Roman numerals?
- When a smaller numeral appears before a larger one, it is subtracted. IV means 5-1=4. XC means 100-10=90. This avoids writing IIII for 4 or LXXXX for 90.
- What is the largest Roman numeral?
- Using standard notation, the largest is MMMCMXCIX = 3999. Some historical texts use a bar over a numeral to multiply by 1000, but this is non-standard.