Roman Numeral Converter

How to use Roman Numeral Converter

1. Choose a direction: number to Roman, or Roman to number.
2. Type the value — 1 to 3999 for numbers, or the numeral for the reverse.
3. Copy the result; the working is shown alongside it.
4. Valid range is 1 to 3999; there is no Roman numeral for zero or for negatives.
5. Only the six standard subtractive pairs are used — IV, IX, XL, XC, CD, CM.
6. Numerals are conventionally written in uppercase; lowercase appears in book prefaces and outline numbering.

The seven symbols and the subtraction rule

I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. Values are added left to right, except that a smaller symbol before a larger one is subtracted: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, CM is 900. Only those six subtractive pairs are valid in the standard form — I can precede only V and X, X only L and C, C only D and M. That is why 99 is XCIX rather than IC, which is the single most common mistake.

Why it stops at 3999

M is the largest symbol, and standard notation allows at most three of any symbol in a row, so MMMCMXCIX — 3999 — is the ceiling. Larger numbers used a vinculum, an overline meaning multiply by a thousand, so V with a bar is 5,000. Since the overline cannot be typed reliably, most converters, including this one, stop at 3999. There is no zero: the concept did not exist in the system, which is one reason Roman arithmetic was so unwieldy and why positional notation displaced it.

Where you still meet them

Clock and watch faces, where 4 is traditionally written IIII rather than IV for visual balance with VIII opposite — an exception so widespread it has its own name, the clockmaker’s four. Film and television copyright dates in end credits. Monarchs and popes. Super Bowl numbering. Book prefaces and outline levels. Chemistry, for oxidation states. And the years on foundation stones, which is how most people end up needing a converter.

Writing a year correctly

Break it into thousands, hundreds, tens and units and write each separately: 2026 is MM + XX + VI = MMXXVI. 1994 is M + CM + XC + IV = MCMXCIV, which packs three subtractive pairs into one year and is the standard worked example. 1888 is the longest year in the common era at MDCCCLXXXVIII, thirteen characters — worth knowing before committing one to a tattoo.