21 = XXI
21 in Roman numerals is XXI.
Twenty-one written with the letters X X I.
21 in words: Twenty-one
Twenty-one in Roman numerals is XXI: two tens (XX) and a one (I), added straight across with no subtraction. Read left to right it is simply ten, twenty, twenty-one, which makes it one of the easier two-digit numerals to write from memory.
XXI carries some cultural weight for such a small numeral. It is the coming-of-age number, the name of the card game, and the way the current century is often styled, the XXI century. That mix of birthday, game and date is why it gets looked up far more than its neighbours.
How 21 breaks down
Reading XXI from left to right, each group is added together to reach 21:
| Group | Value | Place |
|---|---|---|
| XX | 20 | tens |
| I | 1 | ones |
| XXI | 21 | total |
Frequently asked questions
What is 21 in Roman numerals?
21 in Roman numerals is XXI.
How do you write 21 in words?
21 is written "Twenty-one" in English.
What number comes before XXI?
The number before XXI is 20, written XX in Roman numerals.
What number comes after XXI?
The number after XXI is 22, written XXII in Roman numerals.
Related numbers
Last updated July 22, 2026. Reviewed for accuracy against the standard rules for Roman numerals.