Roman Numerals
Type a number to see its Roman numeral, or type a numeral to decode it - both directions update live, with the breakdown shown.
How Roman numerals are built
Roman numerals use seven letters, each with a fixed value: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. You build a number by writing symbols from largest to smallest and adding them up, with one twist: when a smaller symbol sits directly before a larger one, you subtract it. That is why 4 is IV (5 - 1) and 90 is XC (100 - 10).
Reading 1994 = MCMXCIV
Break it into place values and convert each on its own: 1000 is M, 900 is CM, 90 is XC and 4 is IV. Stitch them together and you get MCMXCIV. The converter above shows exactly this split for any number you type, so you can see where each letter comes from.
The subtractive rule and its limits
Only six subtractive pairs are valid: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). You never repeat a symbol four times (so it is IX, not VIIII) and you never subtract across more than one step (so 99 is XCIX, not IC). This converter validates strictly - if you paste a numeral that breaks these rules, it tells you rather than guessing.
Quick reference
| Number | Numeral | Number | Numeral |
|---|---|---|---|
| 1 | I | 40 | XL |
| 4 | IV | 50 | L |
| 5 | V | 90 | XC |
| 9 | IX | 100 | C |
| 10 | X | 500 | D |
| 14 | XIV | 900 | CM |
| 19 | XIX | 1000 | M |
Need to write numbers out in full words instead? Try the number to words converter. Working in other bases? The binary converter handles hex and octal too.