Converts Roman numerals to decimal (base 10) values. The tool validates the input by round-tripping: it converts the Roman numeral to a number, converts back to Roman, and confirms they match. This catches invalid sequences like 'IIII' or 'VV'.
Roman Numeral to Decimal Converter
Convert Roman numerals back to decimal numbers
How to roman numerals to decimal
- 1.Enter a Roman numeral (e.g. XLII) in the input field.
- 2.The decimal equivalent and all other bases appear instantly.
- 3.Both uppercase and lowercase input is accepted.
- 4.Invalid Roman numerals will show an error message.
About This Tool
Frequently Asked Questions
Add the values of symbols from left to right. When a smaller value precedes a larger one, subtract it (IV = 5 - 1 = 4). Otherwise, add it (VI = 5 + 1 = 6).
Invalid patterns include: repeating V, L, or D; more than three consecutive I, X, or C; incorrect subtractive combinations (like IC or XM). The tool detects these by validation.
No — you can enter XLII, xlii, or Xlii. The tool normalises the input to uppercase before processing.