The seven Roman numerals
| I | V | X | L | C | D | M |
|---|---|---|---|---|---|---|
| 1 | 5 | 10 | 50 | 100 | 500 | 1,000 |
How the conversion works
Write the number one place value at a time, from thousands down to ones, using the biggest symbols that fit. Six pairs use subtraction, where a smaller letter goes in front of a bigger one:
Example: 1994. 1,000 + 900 + 90 + 4 = M + CM + XC + IV = MCMXCIV.
Example: 2026. 2,000 + 20 + 6 = MM + XX + VI = MMXXVI.
The rules for a correct numeral
- I, X, C and M can repeat up to three times in a row (III = 3, XXX = 30). V, L and D never repeat.
- Only I, X and C are used to subtract, and only from the next two bigger letters: I from V and X, X from L and C, C from D and M. So 99 is XCIX, not IC, and 49 is XLIX, not IL.
- Letters go from biggest to smallest, except for those subtractive pairs.
The converter checks these rules. If you type a numeral that breaks one, like IIII or IC, it tells you which rule and suggests the standard form. (Clock faces often show IIII for 4. That's a tradition, not the standard form.)
Numbers of 4,000 and up: the overline
A bar over a numeral, called a vinculum, multiplies it by 1,000. So V = 5,000, X = 10,000 and M = 1,000,000. 4,000 is IV, and the largest number with one bar is 3,999,999 = MMMCMXCIXCMXCIX.
The result shows a copy-and-paste version that uses the Unicode combining overline (U+0305), so the bar survives in documents and messages. Not every font draws it neatly. To type one into the converter, use brackets: (IV) means IV. Some writers use M for the 1,000s below 4,000 (so 11,000 could be XM); this converter puts the whole thousands part under one bar.
Limits
- The Romans had no zero and no negative numbers, so the converter takes 1 to 3,999,999.
- Romans themselves weren't always consistent. Old inscriptions include forms like IIX for 8. The converter uses the standard modern rules.