# Roman Numerals

Arabic to Roman number converter

The numbers that we normally use (1, 2, 3 etc) are called "Arabic numerals". But we sometimes use another system for writing numbers - "Roman numerals". The Romans used letters of the alphabet to represent numbers, and you will occasionally see this system used for page numbers, clock faces, dates of movies etc.

Image: On the clockface you see Roman numerals for the hours and Arabic numerals for the minutes.

The letters used in Roman numerals are:

• I = 1
• V = 5
• X = 10
• L = 50
• C = 100
• D = 500
• M = 1000
We can use upper-case letters (capitals) or lower-case letters (small letters) when writing Roman numerals. So the following numbers are exactly the same: XVIII = xviii = 18

In general, letters are placed in decreasing order of value, e.g. XVI = 16 (10+5+1). Letters can be repeated one or two times to increase value, e.g. XX = 20, XXX = 30. Letters cannot be repeated three times, so XXXX is not used for 40. In this case, XL = 40 (50 minus 10).

Do not be fooled by the word repeat, which means "do again". If we write X and then repeat it, we have XX. If we repeat X two times, we have XXX. So XXX is X repeated two times, not three times!

Look at these examples of Roman numerals in use:

• The Introduction is on page vii (= The Introduction is on page 7)

## Significant numbers from one to a thousand

Roman numerals Arabic numerals
upper-case lower-case
I i 1
II ii 2
III iii 3
IV iv 4
V v 5
VI vi 6
VII vii 7
VIII viii 8
IX ix 9
X x 10
XI xi 11
XII xii 12
XIII xiii 13
XIV xiv 14
XV xv 15
XVI xvi 16
XVII xvii 17
XVIII xviii 18
XIX xix 19
XX xx 20
XXI xxi 21
XXII xxii 22
XXIII xxiii 23
XXX xxx 30
XL xl 40
L l 50
LX lx 60
LXX lxx 70
LXXX lxxx 80
XC xc 90
C c 100
CC cc 200
CCC ccc 300
CD cd 400
D d 500
M m 1000