1 - 10

I	II	III	IV	V	VI	VII	VIII	IX	X
I	2	3	4	5	6	7	8	9	10

11 - 20

XI	XII	XIII	XIV	XV	XVI	XVII	XVIII	XIX	XX
11	12	13	14	15	16	17	18	19	20

There are only a few characters in the RN but, unlike Arabic numbers, RN requires the use of addition and subtraction.

The Rules of Roman Numerals
I - This is equal to the count of One. I's are used to represent 2, 3, 4, and eventually 6, 7, 8, 9's. So, two of these I's equal the number 2. Three of these I's represent the number 3, and so on.

V - This represents 5. This character is used three different ways: when the number 4, 5, 6, 7, 8, and 9 are present. To get the number 4, you write IV, therefore it is 5 minus 1 to make 4. However, to get 6, you add 1 instead of subtracting: 5 plus 1. Why? Because the I is in front, adding to the already 5. X - This represents 10. The number 30 would mean XXX. If you would like to have the number 23, you would write XXIII.

L - This represents 50. The number 60 would mean LX while the number 40 would mean XL. To get LX, you add 50 with 10, making it 60. But, just like 5, you only use L for the 40's till the 90's. C - This represents 100. To get 90, you would write XC because you would subtract 10 (represented by X) from 100 (represented by C)