18 in Roman numerals
18 is written XVIII. In chunks: X (10) + V (5) + I (1) + I (1) + I (1) = 18.
The answer
XVIII
18 in Roman numerals is XVIII.
How XVIII is built
To write it, split 18 into 10 + 8. 10 is X, 8 is VIII, so 18 is X then VIII: XVIII.
To read it, XVIII has 5 chunks, and none of them is a take-away pair, so every chunk is added.
| Chunk | Worth | Why |
|---|---|---|
| X | 10 | Add |
| V | 5 | Add |
| I | 1 | Add |
| I | 1 | Add |
| I | 1 | Add |
The mistake to watch for
Writing 18 as XIIX
Wrong: XIIX
XIIX tries to take two I's away from X. Only one smaller letter can go in front of a bigger one, so 8 is VIII (5 + 3), which makes 18 XVIII.
Check it with the converter
Type XIIX to see why XIIX is not 18. The rule numbers it gives are the three rules on the Roman numerals page.
Converter set to XVIII (18).
Keep going
Questions parents ask
What is 18 in Roman numerals?
18 is XVIII.
What comes before and after XVIII?
17 is XVII and 19 is XIX.
Does XVIII use subtraction?
No. Every letter in XVIII is the same size as, or smaller than, the letter before it, so you just add them all.
What is the biggest letter in XVIII?
X, which is 10. XVIII has 5 letters.
Careful reading is an 11+ skill
Reading all 5 letters of XVIII in order is the careful checking 11+ papers reward. The free diagnostic covers all four subjects, with no card needed.