Roman numerals are written using the seven letters of the alphabet in the table below.

There are certain rules when using Roman numerals:

• The letters are arranged from the largest to smallest. The numbers are added to arrive at the value. For example: XVI is X (10) + V (5) + I (1) = 16.
  
  
• When a smaller number preceds a larger number, the smaller is subtracted from the larger. For example:
  
  IX is 1 (I) subtracted from 10 (X) = 9.
  
  
• Do not use the same letter more than three times in a row. You would not, for example, write: CCCC. Rather you would write CD.  C (100) - D (500) = 400.

For a more in depth discussion of Roman numerals, visit the following sites:

NovaRoma
The Ancients Were Mathematicians. Activities, games, worksheets.
Roman Numerals and Dates

1= I
2 = II
3 = III
4 = IV
5 = V
6 = VI
7 = VII
8 = VIII
9 = IX
10 = X
11 = XI
12 = XII
13 = XIII
14 = XIV
15 = XV
16 = XVI
17 = XVII
18 = XVIII
19 = XIX
20 = XX
21 = XXI
22 = XXII
23 = XXIII
24 = XXIV
25 = XXV