Roman Numerals to Numbers

Enter a Roman numeral, and the page shows its value and how it adds up. The reverse direction lives on its own page: numbers to Roman numerals.

How a Roman numeral is read

The symbols go from larger to smaller and add up: XVII is 10 + 5 + 1 + 1, which makes 17. A smaller symbol placed before a larger one is subtracted, and there are only six such pairs: IV (4), IX (9), XL (40), XC (90), CD (400), CM (900). That is why MCMXCIV breaks down as 1000 + 900 + 90 + 4 and equals 1994.

Why IC and IIII are not accepted

Only the next-larger symbol can be subtracted: I is subtracted from V and X, X from L and C, C from D and M. The notation IC looks like 99, but by the rules 99 is written XCIX. The symbols V, L and D are never repeated and never subtracted, while I, X, C and M do not appear more than three times in a row: instead of IIII one writes IV.

You can meet such notations on clock faces and in old inscriptions, but the page refuses to read them on purpose: showing a number for an incorrect notation would reinforce the mistake. Instead of an answer, it tells you how that number is written correctly.

Limit of the notation

With ordinary letters, numbers run from 1 to 3999, the largest being MMMCMXCIX. In antiquity a bar placed above a symbol meant multiplication by a thousand, but such a notation cannot be typed with plain letters. Roman numerals have no zero, and no negative numbers or fractions either.