Roman Numeral Converter
Convert numbers from 1 to 3999 to Roman numerals and validate Roman numerals back to numbers.
🔒 Runs entirely in your browser — nothing is uploadedRoman numeral conversion formula
Roman numerals are built from seven symbols: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. Number-to-Roman conversion repeatedly subtracts the largest symbol value that fits. The ordered formula table is M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I. For example, 2026 subtracts M twice, then XX, then VI, producing MMXXVI. Subtractive pairs such as IV and IX keep the notation compact and standard.
Roman-to-number conversion reads the symbols from left to right. When a smaller value appears before a larger value, it is subtracted; otherwise it is added. IV is 5 − 1 = 4, while VI is 5 + 1 = 6. To validate input, the calculator converts the Roman text to a number and then converts that number back to Roman numerals. The normalized result must match the original.
Valid range and examples
This converter supports standard Roman numerals from 1 through 3999. Larger numbers can be written with overlines in some systems, but those marks are not part of plain keyboard-friendly notation. Valid examples include IX for 9, XLII for 42, XCIX for 99, CDXLIV for 444 and MCMXCIX for 1999. Invalid forms such as IIII, VV, IC or XM are rejected because they do not follow standard subtractive rules.
Uses and privacy
Roman numerals are common in book chapters, outlines, movie credits, clock faces, event names and copyright dates. This page is intended for quick conversion and validation rather than historical typography research. It runs entirely in the browser, does not upload values and does not store a conversion history. Copy the result into your document once it matches the range and validation rules you need.
For publication work, also check the style guide you are following, because some decorative clock faces and legacy inscriptions intentionally use nonstandard forms.
How to use
- Choose directionConvert a number to Roman numerals or Roman numerals back to a number.
- Enter a valid valueNumbers must be from 1 to 3999. Roman numerals are checked for standard subtractive notation.
- Copy the resultUse the converted value and validation message for dates, outlines or labels.