Convert numbers to Roman numerals and vice versa. Learn about the ancient Roman number system.
Roman numerals are mostly additive: symbols from the seven-letter alphabet I, V, X, L, C, D, and M (1, 5, 10,
50, 100, 500, 1000) sum from left to right. The exception is subtractive notation: a smaller symbol placed
before a larger one is subtracted, so IV
is 4, IX is 9,
XL is 40,
XC is 90,
CD is 400, and
CM is 900. Only I, X, and C ever act
as subtractors, which keeps every valid numeral unambiguous.
This converter works in both directions across the standard range of 1 to 3999. Number-to-numeral conversion uses the classic greedy algorithm: it walks a value table that already includes the six subtractive pairs and repeatedly subtracts the largest entry that fits. Roman-to-number parsing scans left to right and subtracts any symbol smaller than its right-hand neighbor, mirroring the same rule in reverse.
The system still appears in copyright lines, book prefaces and chapter numbers, clock faces, and film sequel numbering, which is usually when a quick conversion is needed. All logic runs locally in your browser. For other notation swaps, see the Morse Code Converter, the Text to Binary converter, or the Case Converter for identifier styles.
Standard Roman notation tops out at 3999 (MMMCMXCIX) because 4000 would require four consecutive M symbols, which classic form avoids. Larger numbers were written with an overline, called a vinculum, multiplying the grouped symbols by 1000, and plain text cannot represent that marking.
A smaller symbol placed before a larger one is subtracted instead of added: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, and CM is 900. Only I, X, and C can act as subtractors, and each pairing is fixed, so every valid numeral has exactly one standard reading.
Modern standard form is IV, but IIII survives on traditional clock faces for visual balance around the dial. This converter follows modern conventions and always produces IV.
No. The system has no zero symbol and no place value; counting begins at I. Roman numerals record quantities rather than positional digits, which is why the converter only accepts values from 1 upward.
Yes. Numbers outside 1-3999 and strings containing characters other than I, V, X, L, C, D, and M produce an error message instead of a wrong answer, so a typo cannot silently convert.