Roman numerals
Type in either field and the other fills in. Works for the numbers 1 to 3,999,999.
A whole number from 1 to 3,999,999.
Use I, V, X, L, C, D and M. Write a bar over as (V) or _V.
The building blocks
- I
- IV
- V
- IX
- X
- XL
- L
- XC
- C
- CD
- D
- CM
- M
- IV
- V
- X
- L
- C
- D
- M
How it works
Roman numerals are built from seven symbols: I for 1, V for 5, X for 10, L for 50, C for 100, D for 500 and M for 1,000.
The symbols are written in descending order and added up, so XVII is 10 + 5 + 1 + 1, which is 17.
When a smaller symbol comes before a larger one, it is subtracted instead. That is why IV is 4 and IX is 9. Only I, X and C are used this way, and only before the next two larger symbols.
The same symbol is repeated at most three times in a row, so 4 is written IV, not IIII. For the same reason 4,000 is not written MMMM but with a bar, see the next paragraph.
The system has no symbol for zero or for numbers above 1,000. The Romans wrote larger numbers with a bar over the symbols, the vinculum, which multiplies the value by a thousand: V̅ is 5,000, X̅ is 10,000 and M̅ is 1,000,000. Here the bar is used from 4,000, so 4,000 is I̅V̅ and 14,207 is X̅I̅V̅CCVII. The largest number that can be written this way is 3,999,999.
The bar is not a modern standard. Numbers from 4,000 to 4,999 are also often written with four Ms, such as MMMM for 4,000, even though that breaks the rule of three identical symbols. The tool reads both forms and shows the MMMM form below the result. Because the bar is hard to type on a keyboard, you can also write (V) or _V for V̅.