Roman Numeral to Decimal Converter
Enter a Roman numeral to convert it to a decimal number. Validates the input and handles subtractive notation like IV (4) and IX (9) correctly.
Roman Numeral to Decimal
Base roman → Base 10
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How to Use the Roman to Decimal Converter
1
Enter a Roman numeral (e.g. XLII).
2
Click Convert.
3
View the decimal number.
Frequently Asked Questions
How does Roman-to-decimal conversion work?
Add values left to right. If a smaller value precedes a larger one, subtract it instead (IV = 5-1 = 4).
What Roman numerals are valid?
I, V, X, L, C, D, M and their valid combinations. Invalid sequences will produce an error.
Is the input case-sensitive?
No — both MCMXCIV and mcmxciv are accepted and produce the same result.