How to Convert Roman Numerals

The Seven Roman Numeral Symbols

The whole system rests on just seven letters and their values. I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. Every Roman numeral is built from these letters by combining them. There is no zero and no negative number, which is why the system tops out at 3999 using standard rules.

The Subtractive Rule

When a smaller symbol sits before a larger one, it subtracts instead of adds. That is how 4 becomes IV rather than IIII and 9 becomes IX rather than VIIII. Only three symbols act as subtracting prefixes: I before V and X, X before L and C, and C before D and M. So IL is not a valid way to write 99, because I can only precede V and X.

How to Convert a Number to Roman Numerals

Break the number into place values, convert each chunk separately, then join them. For 2026, split it into 2000, 20, and 6. Two thousands make MM, two tens make XX, and six makes VI, so the answer is MMXXVI. Handle the tricky chunks with subtraction: 4 is IV, 9 is IX, 40 is XL, 90 is XC, 400 is CD, and 900 is CM.

How to Read Roman Numerals Back to a Number

Scan the numeral from left to right and add each symbol, but when a smaller symbol comes before a larger one subtract it. In MCMXCVIII, the M adds 1000, the CM subtracts to give 900, the XC gives 90, and the VIII gives 8, totalling 1998. Grouping the pairs first makes reading long numerals much easier.

Converting Years and Dates

Years are the most common thing people convert. A copyright year, a movie release, or a milestone year such as MMXXIV for 2024 all use the same place value method. Once you can convert a year, the same steps handle any date, chapter number, or clock face numeral you come across.