Roman Numeral Converter
Convert Roman numerals to decimal values or decimal values to Roman numerals.
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Compare Roman numerals and decimal values
XLII ↔ 42
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XLII or 42
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Convert Roman numerals in either direction
Example: XLII ↔ 42
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Understanding Roman Numerals
A System That Endured for Millennia
Roman numerals are a numeral system originating in ancient Rome that remained the dominant way of writing numbers in Europe for nearly two thousand years. Unlike the positional decimal system we use today, Roman numerals use combinations of seven letters from the Latin alphabet: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000).
How Roman Numeral Notation Works
Roman numerals follow two main rules. Additive notation places smaller values after larger ones, and their values are summed: VI equals 5 plus 1, which is 6. Subtractive notation places a smaller value before a larger one to indicate subtraction: IV equals 5 minus 1, which is 4. Only I, X, and C can be used subtractively, and each can only precede the two values immediately above it.
Where Roman Numerals Are Still Used
Despite being over two millennia old, Roman numerals remain common in modern life. They appear on clock faces, in movie and book sequels (Star Wars Episode IV), for monarchs and popes (Queen Elizabeth II), in outlines and legal documents, on building cornerstones to indicate the year of construction, and for Super Bowl numbering. Understanding Roman numerals is therefore a practical skill, not just historical knowledge.
Conversion Tips
When converting from Roman to decimal, read left to right. If a smaller-value symbol appears before a larger-value symbol, subtract it; otherwise, add it. When converting from decimal to Roman, work from the largest value down and repeat symbols as needed, using subtractive pairs for 4s and 9s. This converter handles both directions automatically and validates your input to ensure it follows standard notation rules.