Numbers to Roman Numerals

Enter a regular number, and the page will write it in Roman numerals and show which parts the notation is built from. The reverse direction lives on its own page: convert Roman numerals to numbers.

How the notation is built

The number is broken down from the largest parts to the smallest: thousands first, then hundreds, tens, and units. Each part comes from a ready-made set: M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I. So 2026 is written as MM + XX + V + I, that is, MMXXVI, and 1994 as M + CM + XC + IV.

Four and nine are written by subtraction: IV and IX. The forms IIII and VIIII do not follow the strict rules. The same applies to tens and hundreds: 40 is written XL, 90 is XC, 400 is CD, and 900 is CM. The signs V, L, and D never repeat in a notation; I, X, C, and M never appear more than three times in a row.

Years

A year is written by the same rule, and the length of the notation can be surprising. The longest year in standard notation is 1888, that is, MDCCCLXXXVIII, a full thirteen characters. By contrast, 2000 is written MM, and 1900 is MCM.

What Roman notation cannot do

There is no zero: counting starts from one. It also has no negative numbers and no fractions. The largest number in standard notation is 3999, that is, MMMCMXCIX. In antiquity a line was placed above a sign to mean multiplication by a thousand, but such a notation cannot be typed with ordinary letters.