The below table visualizes how the decimal number 3999 equals the hexadecimal number F9F.
Hexadecimal numbers are a positional numeral system with the base (or "radix") 16. Since there are only 10 different digits, alphabetical letters are used to reach 16 different digits:
|0 - 9||0 - 9|
In the hexadecimal system, the number 16 is written as 10. Hexadecimal numbers are used frequently within computers and programming, since they represent data in a more human-readable way than binary digits do. One hexadecimal digit represents four binary digits, and thus two hexadecimal digits together describe one Byte. One Byte can represent all numbers between 00 and FF in the hexadecimal format. An example of when this is used in programming is color codes, for example in CSS on a website, where hexadecimal numbers can be used to define the three color components Red, Green and Blue (#RRGGBB). Some examples below: