Roman Numeral Converter
One box for both directions: digits become Roman numerals, letters become a number.
How the conversion works
Split the number into thousands, hundreds, tens and units, and write each place on its own, from left to right. Every place uses the same pattern with different letters: 1–3 repeat the one (I, II, III), 4 is one before five (IV), 5–8 start from five (VI, VIII) and 9 is one before ten (IX).
Take 1994. One thousand is M, nine hundred is CM, ninety is XC and four is IV. Put them together and you get MCMXCIV. Going the other way, read left to right and subtract a letter only when a larger one follows it.
The seven letters and the six pairs
Only six subtractive pairs exist: IV, IX, XL, XC, CD and CM. A letter can repeat at most three times in a row, and V, L and D never repeat. The guide to the rules explains why.
- I1
- V5
- X10
- L50
- C100
- D500
- M1,000
- IV4
- IX9
- XL40
- XC90
- CD400
- CM900
Examples
Each row is converted by the same code as the box above. Numbers with their own page are linked.
| Number | Roman numeral | How it reads |
|---|---|---|
| 7 | VII | VII (7) |
| 20 | XX | XX (20) |
| 49 | XLIX | XL (40) + IX (9) |
| 99 | XCIX | XC (90) + IX (9) |
| 198 | CXCVIII | C (100) + XC (90) + VIII (8) |
| 444 | CDXLIV | CD (400) + XL (40) + IV (4) |
| 1980 | MCMLXXX | M (1000) + CM (900) + LXXX (80) |
| 1994 | MCMXCIV | M (1000) + CM (900) + XC (90) + IV (4) |
| 2014 | MMXIV | MM (2000) + X (10) + IV (4) |
| 3999 | MMMCMXCIX | MMM (3000) + CM (900) + XC (90) + IX (9) |
When the converter says no
- Four of the same letter, like IIII or XXXX: the standard form is IV and XL. Clock faces are a known exception (source: en.wikipedia.org).
- A jump in subtraction, like IL for 49: only I, X and C subtract, and only from the next two letters, so 49 is XLIX.
- The digit 1 or a lowercase l mixed in: MMXV1 is not a numeral. The validator points to the character that breaks the rule.
- Zero and negative numbers: the system has no zero, so the converter starts at 1.
Numbers above 3,999
Without extra marks, the largest Roman numeral is MMMCMXCIX. Tick "Numbers above 3,999" to use the bar (vinculum): a line over a group multiplies it by 1,000, so 5,000 is V̅ and 2,026,000 is M̅M̅X̅X̅V̅I̅. Copied text keeps the bar as a combining character, which some fonts draw slightly off. The guide to large numbers covers the other notations.
Common questions
What is the largest number you can write in Roman numerals?
With the seven letters alone, MMMCMXCIX (3,999). With a bar over the thousands, the converter goes up to 3,999,999.
Is there a zero in Roman numerals?
No. There is no letter for zero, so the converter accepts numbers from 1 up.
Why does the converter reject IIII or IL?
They break the standard rules: a letter repeats at most three times, and I only subtracts from V and X. The standard forms are IV and XLIX.
Can I paste lowercase letters or characters like Ⅻ?
Yes. Lowercase is read as uppercase, spaces are ignored, and the single-character numerals Ⅰ to Ⅿ are read as ordinary letters.