Roman Numeral Converter

This converter translates in both directions: type a whole number from 1 to 3999 and it returns the Roman numeral, or type Roman numeral text and it returns the ordinary decimal number. Roman numerals are an ancient system of writing numbers that originated in the Roman Empire and remained the standard across Europe for centuries. They are still very much alive today, which is why being able to read and write them is genuinely useful rather than just a historical curiosity. The system is built from just seven letters combined according to a small set of rules, and once those rules are clear the conversions become straightforward.

The Seven Symbols

Everything is built from seven capital letters, each standing for a fixed value: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1000. A handy way to remember the order is the phrase "I Value Xylophones Like Cows Drink Milk." In the usual case, symbols are written from the largest value on the left to the smallest on the right, and you simply add them up. So MMXVI is 1000 + 1000 + 10 + 5 + 1 = 2016, and CCLXVII is 100 + 100 + 50 + 10 + 5 + 1 + 1 = 267.

The Additive and Subtractive Rules

Two rules govern how symbols combine. The additive rule says that when a symbol is followed by one of equal or smaller value, you add them — XV is 10 + 5 = 15. To keep numerals short, a symbol that represents a power of ten (I, X, C, M) may be repeated at most three times in a row; III is valid for 3, but IIII is not the correct form for 4. That limit is where the subtractive rule comes in: when a smaller-value symbol is placed immediately before a larger one, it is subtracted rather than added. There are exactly six legal subtractive pairs: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, and CM = 900. Notice the pattern: I subtracts only from V and X, X subtracts only from L and C, and C subtracts only from D and M. Each symbol may only be subtracted from the next one or two higher symbols — never further. The five-value symbols V, L, and D are never used subtractively and are never repeated.

A Worked Example

Let us convert 1994 to a Roman numeral step by step, always taking the largest chunk possible. Start with the thousands: 1994 contains one 1000, which is M, leaving 994. The next largest piece is 900, written with the subtractive pair CM, leaving 94. Then 90 is XC, leaving 4. Finally 4 is IV. Putting the pieces in order gives MCMXCIV. Reading it back confirms the logic: M (1000) + CM (900) + XC (90) + IV (4) = 1994. This is exactly how the year 1994 appears in film credits and copyright lines. Converting in the other direction works the same way in reverse: scan left to right, add each symbol, but subtract whenever a smaller symbol sits in front of a larger one.

Tips and Common Mistakes

A few rules trip people up most often. Do not stack subtractions: 99 is not IC, it is XCIX (90 + 9); subtraction only ever uses a single smaller symbol before a single larger one. Do not over-repeat: 40 is XL, never XXXX, and 4 is IV, never IIII (the IIII seen on some clock faces is a decorative exception, not the standard form). Keep symbols in descending order apart from the six valid subtractive pairs — VX, IL, and similar combinations are invalid. There is also no symbol for zero in the Roman system and no way to write negative numbers or fractions in everyday notation, which is one reason the modern decimal system eventually replaced it. If you enter text that breaks any of these rules, this converter flags it as invalid so you can correct the order or spelling.

The 1 to 3999 Range

This tool covers the standard range of 1 to 3999. The lower limit exists because there is no Roman numeral for zero or for negative values. The upper limit comes from the three-repeat rule applied to M: the largest number you can build with up to three M's plus the rest is 3999 (MMMCMXCIX). To go higher, the Romans drew a horizontal bar (a vinculum) over a numeral to multiply it by 1000, but that overline cannot be represented in ordinary text, so 1 to 3999 is the universally agreed practical range — and it comfortably covers years, chapter numbers, monarchs, and event editions.