821 in Roman numerals

821 in Roman numerals is DCCCXXI.

Pick any whole number from 1 to 3,999.

821 = \text{DCCCXXI}

How to work it out

1
Take the biggest Roman value that fits, write its letter, subtract it, and repeat.
2
Here: 500 (D) + 100 (C) + 100 (C) + 100 (C) + 10 (X) + 10 (X) + 1 (I) = 821.
3
Joined together: DCCCXXI. (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 821 in Roman numerals?

DCCCXXI.

How do you read DCCCXXI?

DCCCXXI = 500 + 100 + 100 + 100 + 10 + 10 + 1 = 821.