18 in Roman Numerals

How to write 18 in Roman numerals

Roman numerals are built place by place, from the largest value to the smallest. For 18 the places are 10 (tens), 8 (ones).

1. Write 10 as X.
2. Write 8 as VIII.

Joined together, X + VIII gives XVIII.

18 digit by digit

Check XVIII by reading it back

Reading XVIII from left to right and adding the pieces: X = 10, VIII = 8. Together that is 10 + 8 = 18, so XVIII and 18 match.

Mistakes to avoid with XVIII

• Never repeat a symbol more than three times in a row. When a fourth would be needed, the subtractive form takes over.
• Only I, X and C may be placed before a larger symbol to subtract, so XVIII never contains forms such as VX or LC.
• Read XVIII as one number, not letter by letter: add the values left to right, except where a smaller symbol sits before a larger one.

Facts about the number 18

• 18 is an even number and composite, with prime factors 2 x 3².
• In binary 18 is 10010 and in hexadecimal it is 12.
• Written out, 18 is "eighteen".
• The digits of 18 add up to 9, so it is divisible by 3.

Where you will see 18 in Roman numerals

The number 18 shows up as XVIII when referring to the eighteenth century in history books. Golf tournaments occasionally use it for hole markers. Authors choose this arrangement of five letters to clearly denote a specific hundred year period while maintaining a formal academic tone throughout their writing.

Numbers near 18

More roman numerals

• 17 (XVII): previous page
• 19 (XIX): next page
• Roman numerals chart: the full list