Revised 5/11 1
HFCC Math Lab NAT – 07
Converting Roman Numerals to Arabic Numerals
Face value of Roman numerals
Some often used characters in Roman numerals and their face value listed below:
Using these characters you can write any positive number from 1 up to 4,999,999. To represent higher
numbers you introduce characters similar to one on the second column with more bars. For example, five
million is represented by the character
Place value of Roman numerals
Every roman numeral is written as a string of characters. To find the Arabic numeral corresponding to the
given Roman numeral, write down the face value of every character in the given string and then either add or
subtract the face value.
To determine when to add the value and when to subtract the value, use the following rules:
• Start converting Roman numerals to Arabic numerals from left to right.
• If the face value of a character is smaller than the character following it, subtract the first character.
Otherwise add the first character.
• Always add the last character in the string.
Example 1: Roman numeral XI translates as +10 +1 = +11 in Arabic numerals. Since the face value
of X is higher than face value of I, we add the face value of X to the face value of the last character I
Example 2: Roman numeral IX translates as –1 +10 = +9 in Arabic numerals. Since the face value
of I is smaller than face value of X, we subtract the face value of I from the face value of the last