999 in Roman numerals

999 in Roman numerals is CMXCIX.

Pick any whole number from 1 to 3,999.

999 = \text{CMXCIX}

How to work it out

1
Take the biggest Roman value that fits, write its letter, subtract it, and repeat.
2
Here: 900 (CM) + 90 (XC) + 9 (IX) = 999.
3
Joined together: CMXCIX. (Four of the same letter in a row is never used: 4 is IV, 9 is IX, 40 is XL, 90 is XC, 400 is CD, 900 is CM.)

What is 999 in Roman numerals?

CMXCIX.

How do you read CMXCIX?

CMXCIX = 900 + 90 + 9 = 999.