Roman Numerals - Reading Roman Numerals

Reading Roman Numerals

Roman numerals, as used today, are based on seven symbols:

These Roman numbers are formed by combining symbols together and adding the values. For example, MMVI is 1000 + 1000 + 5 + 1 = 2006. Generally, symbols are placed in order of value, starting with the largest values. When smaller values precede larger values, the smaller values are subtracted from the larger values, and the result is added to the total. For example MCMXLIV = 1000 + (1000 − 100) + (50 − 10) + (5 − 1) = 1944.

Below are some examples of the modern use of Roman Numerals.

• 1910 as MDCCCCX (Admiralty Arch in London)
• 1954 as MCMLIV (Trailer for the movie The Last Time I Saw Paris)
• 1990 as MCMXC (The title of musical project Enigma's debut album MCMXC a.D., named after the year of its release.)

There has never been a universally accepted set of rules for Roman numerals. Because of this lack of standardization, there may be multiple ways of representing the same number in Roman numerals. For example, the United States National Institute of Standards and Technology could find no authority that could describe if the year 1999 should be written as MDCCCCLXXXXVIIII, MCMXCIX, or MIM. Despite the lack of standardization, an additional set of rules has been frequently applied for the last few hundred years:

• A number written in Arabic numerals can be broken into digits. For example, 1903 is composed of 1 (one thousand), 9 (nine hundreds), 0 (zero tens), and 3 (three units). To write the Roman numeral, each of the non-zero digits should be treated separately. In the above example, 1,000 = M, 900 = CM, and 3 = III. Therefore, 1903 = MCMIII.
• The symbols "I", "X", "C", and "M" can be repeated three times in succession, but no more. (They may appear more than three times if they appear non-sequentially, such as XXXIX.) "D", "L", and "V" can never be repeated.
• "I" can be subtracted from "V" and "X" only. "X" can be subtracted from "L" and "C" only. "C" can be subtracted from "D" and "M" only. "V", "L", and "D" can never be subtracted
• Only one small-value symbol may be subtracted from any large-value symbol.