Roman Numerals Converter

How do Roman numerals work?

Seven letters hold up the whole system: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). When a smaller letter sits before a larger one, it subtracts, and that is how we get 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD) and 900 (CM).

Values run from 1 up to 3999 (MMMCMXCIX). Worth remembering that the classical Roman system had no zero and no negative numbers.

Roman numerals: symbols and rules

Roman numerals use seven symbols: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Values are written from largest to smallest and added together — MCLXVI = 1000+100+50+10+5+1 = 1166. When a smaller symbol appears before a larger one, it is subtracted: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Example: MCMXCIX = 1000 + (1000−100) + (100−10) + (10−1) = 1999.

Rules: never repeat the same symbol more than three times in a row (4 is IV, not IIII — although clock faces traditionally use IIII for visual symmetry); only I, X and C can be used subtractively, and only before the next two larger symbols (I before V or X; X before L or C; C before D or M). There is no zero in Roman numerals. The practical limit is 3999 (MMMCMXCIX); larger numbers use a vinculum — a bar above the symbol that multiplies its value by 1000.

Where Roman numerals still appear

Book prefaces and chapter numbering, names of kings and popes (Louis XIV, John Paul II), Super Bowl editions (LVIII = 58), Olympic Games, clock and watch faces, copyright dates in films and TV credits (MCMXCIX = 1999), monuments and cornerstones, outlines and legal documents. They survive because they look formal and visually distinguish enumerated items from cardinal numbers.