How do I read and write Roman numerals?
A numeral is a symbol used to represent a number. (Our digits 0-9 are often called Arabic numerals.) Each letter used in Roman numerals stands for a different number:
Roman Numeral
Number
I
1
V
5
X
10
L
50
C
100
D
500
M
1000
A string of letters means that their values should be added together. For example, XXX = 10 + 10 + 10 = 30, and LXI = 50 + 10 + 1 = 61. If a smaller value is placed before a larger one, we subtract instead of adding. For instance, IV = 5 - 1 = 4.
You can use these rules to write a number in Roman numerals. Convert one digit at a time. Let's try 982:
982
= 900 + 80 + 2
= CM + LXXX + II
= CMLXXXII.
Here are the official rules for subtracting letters:
Subtract only powers of ten, such as I, X, or C. Writing VL for 45 is not allowed: write XLV instead.
Subtract only a single letter from a single numeral. Write VIII for 8, not IIX; 19 is XIX, not IXX.
Don't subtract a letter from another letter more than ten times greater. This means that you can only subtract I from V or X, and X from L or C, so MIM is illegal.
These rules only became official in the Middle Ages. Even today, not everybody follows them: you might notice that some clocks say IIII instead of IV.
The biggest Roman numeral is M, for 1000, so one easy way to write large numbers is to line up the Ms: MMMMMMM would be 7000, for instance. This system gets cumbersome quickly. When they needed to work with many large numbers, the Romans often wrote a bar above a numeral. The bar meant to multiply by 1000. Using this method, 7000 would be VII with a line on top.
