Which number base does hexadecimal use?

Hexadecimal counts in base sixteen, mixing the Greek hexa for six with the Latin decim for ten. Because there are only ten digit symbols available, the letters A through F stand in for the values ten through fifteen, so the sequence runs 8, 9, A, B, C, D, E, F and then 10, which means sixteen. Programmers use it constantly for one reason: sixteen is two to the fourth power, so every hex digit maps exactly onto four binary digits, and a byte of eight bits is written as precisely two hex characters. That makes long binary strings readable without losing any structure, and it is why memory addresses, error codes and colour values are shown in hex. A web colour like FF0000 is simply full red with no green or blue, each pair of characters covering the range zero to 255. Octal, base eight, was used for the same purpose on older machines with different word sizes.

Counting on the finger bones of one hand rather than the fingers themselves gives twelve, which is one theory for the persistence of dozens.