Convert any Roman numeral to its Arabic (decimal) equivalent instantly. Type any Roman numeral from I to MMMCMXCIX (1 to 3,999) and the converter shows the number in real time with validation. All conversion runs locally in your browser.
To convert a number to Roman numerals, the tool repeatedly subtracts the largest possible Roman numeral value from the number and appends the corresponding symbol (including subtractive pairs like IV=4, IX=9, XL=40, XC=90, CD=400, CM=900). To convert Roman numerals to a number, each character is mapped to its value; a character is subtracted if the next character has a greater value. All processing runs in JavaScript in your browser.
All conversions happen locally in your browser tab. Our servers are not involved at any point.
For working with fractional or mixed numbers, try the fraction calculator. To convert numbers between binary, hex, and decimal, use the number base converter. For unit conversions like inches to centimetres, see the unit converter.