Roman numerals converter

Seven letters, added up

Roman numerals use seven symbols:

Written from largest to smallest, the values simply add up. MDCCLXXVI is M (1000) + D (500) + CC (200) + L (50) + XX (20) + V (5) + I (1) = 1776. To write a number, take it apart by place value and write each part: 2026 is 2000 + 20 + 6, so MM + XX + VI = MMXXVI.

No symbol is used more than three times in a row, and V, L and D are never repeated at all, since VV would just be X. That limit is why 4 is not written IIII in the standard form, and why the system stops at 3999: 4000 would need a fourth M. The Romans themselves were not consistent: inscriptions show both IIII and IV, and the strict rules were settled long afterwards.

The six subtractive pairs

When a smaller symbol comes before a larger one, it is subtracted. Only six such pairs are allowed:

The rules behind the list: only I, X and C can be subtracted; each only from the next two symbols up (I from V and X, X from L and C, C from D and M); and only one at a time. So 49 is XLIX (40 + 9), not IL; 99 is XCIX, not IC; 8 is VIII, not IIX; and 1999 is MCMXCIX, not MIM. Octoolo applies these rules strictly when it reads a numeral, so one that breaks a rule is reported instead of guessed at. That also makes it a quick way to check a numeral you have written yourself.

A long numeral is easiest to read in chunks: MCMXCIX splits into M, CM, XC and IX, which is 1000 + 900 + 90 + 9. Writing works the same way in reverse, one digit at a time: for 3449, 3000 is MMM, 400 is CD, 40 is XL and 9 is IX, so 3449 is MMMCDXLIX.

Where Roman numerals still show up

• Years. Film credits, cornerstones and copyright lines: 1984 is MCMLXXXIV, 2000 is MM, 2026 is MMXXVI.
• Events. The Super Bowl played in February 2026 was Super Bowl LX, number 60.
• Names. Kings, queens and popes: Elizabeth II, Louis XIV.
• Sequels and editions. Films, games and book volumes: Part II, Volume IV.
• Documents. Outline headings, volume numbers and the front pages of books, usually in lower case: page xii is page 12.
• Clocks and watches. Many show 4 as IIII, a long tradition. The converter follows the standard rules, so it treats IIII as invalid; IV is the standard form.
• Engraving and tattoos. Dates are usually written with dots or spaces between the parts, such as XV · VI · MCMXC for 15 June 1990. Convert each part on its own.

Numbers with no Roman form

Some numbers simply cannot be written in standard Roman numerals. There is no numeral for zero, and none for negative numbers or decimals; the Romans wrote fractions as twelfths with signs of their own, which the converter does not read. Above 3999, Romans and later scribes used extra marks, such as a bar over a numeral to multiply it by 1,000, but there was never one agreed system, so the converter stops at MMMCMXCIX.

The longest numeral in range belongs to 3888: MMMDCCCLXXXVIII, fifteen letters. Unicode also has special Roman numeral characters, such as Ⅻ, but they are rarely used; the converter reads ordinary letters. If you need to turn a number into binary or hexadecimal instead, the number base converter in the Dev Toolbox does that.