Roman numerals

Roman Numerals

Roman numerals aren’t used much in modern computing, and they’re tricky to understand. Interestingly, they don’t include a zero, or do they?

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

1
2
3
4
5
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7
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Symbol       Hindu Equivalent
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

Rules

• Typically, Roman numerals are written from largest to smallest, left to right.
• Repeating a numeral up to three times indicates addition, such as III for 3 (1 + 1 + 1).
• Only I, X, C, and M can be repeated; V, L, and D cannot.
• Numerals in decreasing order from left to right are additive: LX for 60 (50 + 10), XVI for 16 (10 + 5 + 1).
• To avoid repeating a numeral four or more times, smaller numerals placed before larger ones indicate subtraction, like IV for 4 (5 - 1) or IX for 9 (10 - 1). Only specific numeral pairs use this rule.

Examples

For instance, 2 is written as II, combining two ones. 12 is XII, and 27 is XXVII.

The numeral for four is not IIII, but IV, indicating subtraction. Similarly, nine is written as IX. Specific subtraction rules are:

• I before V (5) and X (10) makes 4 and 9.
• X before L (50) and C (100) makes 40 and 90.
• C before D (500) and M (1000) makes 400 and 900.

Some more examples:

Full List

Here is the list: