About Roman Numerals
Rome's numbers never fully retired: they mark movie and TV production years (the credits' MMXXVI), Super Bowls, monarchs and popes, book prefaces, clock faces, and building cornerstones. Reading them fluently is a small skill that pays off constantly; writing them correctly — with the subtractive rules — is where most people slip.
Convert either direction: type a number (1–3999) for its numeral with the build shown symbol group by symbol group, or paste a numeral to read its value — including non-standard but readable forms like IIII, which the converter accepts and gently corrects to canonical form.
Working between number systems generally? Decimals live in the Decimal Calculator.
The Rules
Three rules generate every standard numeral:
1. Add symbols left to right, largest first: MMXXVI = 1000+1000+10+10+5+1 2. Never repeat a symbol 4×: use the subtractive pairs IV=4 IX=9 XL=40 XC=90 CD=400 CM=900 3. Only I, X, C subtract — and only from the next two steps up
Worked example: 1999 = M (1000) + CM (900) + XC (90) + IX (9) = MCMXCIX — famously NOT MIM, because I may only subtract from V and X. And 2026 is simply MMXXVI: two thousands, two tens, five, one.
Symbols & Landmark Numbers
The seven symbols and the conversions people actually look up:
| Symbol | Value | Number | Numeral |
|---|---|---|---|
| I | 1 | 4 | IV |
| V | 5 | 9 | IX |
| X | 10 | 40 | XL |
| L | 50 | 49 | XLIX |
| C | 100 | 90 | XC |
| D | 500 | 1999 | MCMXCIX |
| M | 1,000 | 2026 | MMXXVI |
| — | — | 3,999 | MMMCMXCIX (the maximum) |
Mnemonic for the ladder: “I Value Xylophones Like Cows Do Milk” — I, V, X, L, C, D, M.
Quirks Worth Knowing
Clock faces often show IIII instead of IV — a centuries-old convention variously explained by visual balance with VIII opposite it, tradition, and (per legend) royal preference. It's non-standard but universally understood; this converter reads IIII as 4 and notes the canonical form. Similarly, old texts sometimes use additive forms (VIIII for 9) that read fine but wouldn't be written today.
There's no zero (the concept post-dates the system — Romans wrote “nulla”), no fractions in common use beyond twelfths, and no standard form above 3,999 without the vinculum overline. That's why Super Bowl 50 broke tradition and used the digits — the NFL blinked at “Super Bowl L.”