Number
991 in Roman numerals
991 is written CMXCI
Type any other number or numeral below to convert it.
Above 3,999? Type the barred part in brackets, e.g. (IV)CC = 4,200.
How CMXCI is built
Roman numerals are written one decimal place at a time, largest first.
- CMhundreds · 9C before M means 1,000 − 100 = 900. This saves writing DCCCC.
- XCtens · 9X before C means 100 − 10 = 90. This saves writing LXXXX.
- Iones · 1I is 1.
900 + 90 + 1 = 991
The pairs CM and XC use subtraction: a smaller letter before a larger one is taken away from it. Only six pairs work this way: IV, IX, XL, XC, CD and CM. More on subtraction
Mistakes to avoid
- Not XMI. It looks like a shortcut, but X may only come before L or C, not M. The correct form is CMXCI.
- Not DCCCCLXXXXI (11 letters). That adds everything up without subtraction. The Romans sometimes wrote numbers this way, and clocks still show 4 as IIII, but today CMXCI (5 letters) is the standard.
About the number 991
- 991 is a prime number: only 1 and 991 divide it exactly.
- CMXCI has 5 letters. 604 of the numbers up to 1,000 have longer numerals.
Counting from 991 to 1,000
| Number | Roman numeral |
|---|---|
| 991 | CMXCI |
| 992 | CMXCII |
| 993 | CMXCIII |
| 994 | CMXCIV |
| 995 | CMXCV |
| 996 | CMXCVI |
| 997 | CMXCVII |
| 998 | CMXCVIII |
| 999 | CMXCIX |
| 1,000 | M |