Roman Numeral Converter
Convert Arabic integers to Roman numerals and Roman numerals back to numbers, with validation for the 1 to 3999 range.
Roman Numeral Converter — Convert whole numbers into Roman numerals and decode Roman numerals back into ordinary numbers, in either direction. Pick the direction, type your value, and the result appears instantly with on-the-fly validation that flags out-of-range numbers and malformed numerals. Everything runs entirely in your browser, so the values you type never leave your device.
What is Roman Numeral Converter?
The Roman Numeral Converter is a free in-browser tool that translates between Arabic integers and standard Roman numerals in both directions. Students, history and Latin learners, designers picking copyright dates or clock faces, and writers naming chapters, monarchs, and editions use it to read or write numerals correctly. Choose Number to Roman to turn an integer from 1 to 3999 into numerals like MMXXVI, or choose Roman to Number to decode a numeral such as XIV back to 14. The tool uses the standard subtractive notation (IV, IX, XL, XC, CD, CM), checks that your Roman input is a well-formed numeral, and limits numbers to the classic 1 to 3999 range. An optional setting outputs the numerals in uppercase or lowercase.
How to use Roman Numeral Converter
- Choose a direction with the segmented control: Number to Roman or Roman to Number.
- For Number to Roman, type a whole number from 1 to 3999 into the input field.
- For Roman to Number, type a Roman numeral such as MMXXVI (letters M, D, C, L, X, V, I).
- Read the converted result in the read-only output field; it updates automatically as you type.
- Open Settings to switch the Roman output between uppercase (XIV) and lowercase (xiv).
- Use the copy button to copy the result, or Clear to empty the input.
Examples
Number to Roman: a recent year
Input
Direction: Number to Roman, 2026
Output
MMXXVI
Roman to Number: a chapter numeral
Input
Direction: Roman to Number, XIV
Output
14
Subtractive notation
Input
Direction: Number to Roman, 49
Output
XLIX
Frequently asked questions
- What range of numbers is supported?
- Standard Roman numerals cover 1 to 3999. The tool accepts whole numbers in that range; values below 1, above 3999, or with decimals are rejected with an error message, because classical numerals have no symbol for zero or for thousands beyond 3999.
- How are 4 and 9 written?
- The converter uses subtractive notation: 4 is IV (not IIII) and 9 is IX, 40 is XL, 90 is XC, 400 is CD, and 900 is CM. Decoding accepts these standard forms and validates that the numeral is well-formed.
- Does it accept lowercase Roman numerals?
- Yes. When decoding, you can type numerals in upper or lower case (xiv or XIV) and the value is read the same way. When encoding, an optional setting outputs the numerals in uppercase or lowercase.
- What happens if I enter an invalid numeral?
- If a Roman numeral is malformed (for example IIII or VX) or a number is out of range, the output stays a dash (—) and a clear error note explains the problem until you fix the input.
- Is my data sent to a server?
- No. Every conversion runs 100% client-side in your browser with no upload and no server communication, so the values you enter never leave your device.
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