Roman Numeral to Number Converter

About this calculator

Roman numerals build numbers from seven symbols — I=1, V=5, X=10, L=50, C=100, D=500, M=1000 — normally added together left to right, but with a subtractive rule where a smaller symbol placed before a larger one is subtracted instead (IV = 4, IX = 9, XL = 40, CM = 900). Converting the other direction, from an integer to Roman numerals, works by greedily subtracting the largest possible symbol value (including the subtractive pairs) until nothing remains — standard Roman numerals cover integers from 1 to 3999.

Students learning the numeral system, programmers implementing or testing the conversion algorithm, and anyone decoding a copyright year in film credits, a clock face, or a book chapter number use this converter to move between the two number systems instantly.