Roman numerals use seven capitalized letters from the alphabet. The letters, which are I, V, X, L, C, D and M, are typed on a standard keyboard by pressing the shift key plus a letter or by enabling caps lock before keying a series of letters.

Roman numerals use a combination of letters to denote specific values. Each of the seven letters corresponds to a numerical value: I for one, V for five, X for ten, L for fifty, C for 100 and M for 1,000. Zero has no Roman numeral representation.

Combine and arrange the letters in particular order to symbolize numbers. Roman numerals written in groups are added together, therefore, II is equivalent to two because I + I = 1 + 1 = 2. A letter can only be repeated three times; thus, III represents three but, IIII cannot represent four. Four is characterized by IV because Romans made the rule that a smaller numeral before a larger numeral means the smaller numeral will be deducted from the larger numeral.

This system can only represent numbers up to 3,999. To represent larger numbers, a horizontal line over a numeral is used to multiply that specific number by one thousand. Additional vertical lines before and after a numeral are used to denote numbers up to millions.