Roman Numeral Calculator – Convert Numbers and Roman Numerals
Free Roman numeral converter: convert numbers 1–3999 to Roman numerals and Roman numerals to numbers. Bidirectional conversion. Useful for clocks, outlines, and historical notation. No sign-up, runs in your browser.
Roman Numeral Calculator
Convert between numbers and Roman numerals. Numbers 1–3999 supported.
How Roman numerals work
Roman numerals use letters: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Values are added left to right, except when a smaller numeral precedes a larger one (subtraction): IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. The calculator validates both number-to-Roman and Roman-to-number conversions.
Example: 2024 = MMXXIV (M+M+X+X+IV)
When and why to use a Roman numeral converter
Roman numerals are still used today: on clock faces, in book chapters and outlines, for copyright years (e.g. MMXXIV), and in formal numbering. They also appear in chemistry (oxidation states) and in historical or ceremonial contexts. Converting between Arabic numbers and Roman numerals by hand can be tedious, especially for larger values.
This calculator handles both directions. Enter a number (1–3999) to get the Roman form, or enter a valid Roman numeral to get its decimal value. It validates input and rejects invalid sequences. For other number systems like binary or hex, use our binary calculator or hex calculator.
This tool runs in your browser and does not store your inputs. It supports the standard subtractive notation (IV, IX, XL, XC, CD, CM) and rejects invalid Roman numeral sequences.