Roman Numerals were used in ancient Rome to write numbers through a combination of seven letters from the Latin Alphabet. Roman numerals are the symbols I, V, X, L, C, D, and M, which represent the numbers 1, 5, 10, 50, 100, 500, and 1,000 respectively.
To understand and convert Roman Numerals to the Decimal Number System, we need to learn what each letter represent and know the different rules in writing the letters.
Rules for Roman Numerals
- A symbol placed after another of equal or greater value adds its value. For example: II = 2 and XV = 15.
- A symbol placed before one of greater value subtracts its value. For example, IV = 4, IX = 9, XL = 40, and CD = 400.
- A bar placed over a number multiplies its value by 1,000.
- Roman numerals cannot be written together more than 3 times. For example, the number 40 is not XXXX. It is written as XL, instead.
Converting Roman Numerals Examples
Example 1: XVI
First step is to expand the letters to their decimal value. Thus X, V, and I, means 10, 5 and 1. Since the arrangement is from highest value to the lowest value, we simply add them. Thus
XVI = 10 + 5 + 1 = 16
Example 2: LXXIV
Let’s expand the letters to their decimal value first. LXXIV are 50, 10, 10, 1 and 5. The LXX are in ascending order, so we just add them. But, notice that the 1 and 5 are not in ascending order, thus, we subtract them. Therefore,
LXXIV = 50 + 10 + 10 + (5-1) = 74
Example 3: Convert 1975 to Roman Numerals
First step is to break down the number 1975 to its place values.
1975 = 1000 + 900 + 70 + 5
Then convert each place value to Roman Numerals
1000 is M
900 is CM
70 is LXX
5 is V
Thus,
1975 = MCMLXXV
Roman Numeral Worksheets
Below are worksheets to practice converting Roman Numerals to Numbers, and vice versa.
More about Roman Numerals
- Visit our Roman Numerals Page for lessons, tips and free worksheets to download.
- Use this online converter to change Roman Numerals to Decimal Numbers.
