How to Convert Roman to Arabic Numerals
We all learned about Roman numerals in third-grade math, but since most of us don't see Roman numerals every day, we are lost when the time comes to puzzle out the copyright date of an old film, or read a monumental inscription. However, converting Roman numerals to Arabic numerals is easy; you just have to remember the numerical value of seven signs and a few simple rules.
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Instructions
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Memorize the numerical value of the Roman numerals: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1000.
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Decipher value further by reading the numerals' position. In general, the signs are written in descending order of value, starting on the left (the same as Arabic numerals). Therefore, 1217 is written as MCCXVII. However, numbers can be used in a subtractive fashion, if they are positioned to the left of a larger number. For instance, 1900 would ordinarily be written MCM, not MDCCCC. This keeps numbers from getting unwieldy.
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Learn the two ways in which larger numbers were represented. To indicate that a number should be multiplied by a thousand, Romans used a bar above the numeral, and to indicate a multiple of 100,000, they added a bar on either side (the numeral then appeared to be in a three-sided box, open on the bottom).
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4
Convert Roman fractions to Arabic numerals by remembering the signs S (1/2) and -- (1/12). The number of horizontal strokes indicates the fraction of 12. For example, = -- equals 3/12. For numbers greater than 1/2, S and -- were used in combination: S = = -- equals 11/12.
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Tips & Warnings
Any time a numeral is in a position other than the expected descending order of value, subtract it from the numeral it immediately precedes.
In ancient documents and inscriptions, the convention of using the subtractive method instead of having four of the same symbol in a row was not always observed. Therefore, you could occasionally see IIII and IV in the same document, both meaning 4.
