It's a handy way of expressing byte values. Expressing in binary is too verbose and in decimal it is tedious to convert from and to it.

A hexadecimal value can range from $00_{16}$ to $FF_{16}$.

Hex digit	Decimal value	Binary value
0	0	0000
1	1	0001
2	2	0010
3	3	0011
4	4	0100
5	5	0101
6	6	0110
7	7	0111
8	8	1000
9	9	1001
A	10	1010
B	11	1011
C	12	1100
D	13	1101
E	14	1110
F	15	1111

Hex to/from binary

Just remember that each Hex digit represents 4 bits in binary.

Binary to Hex

Hex to Binary

Same as the above but starting from the bottom instead of from the top.

Hex to/from decimal

This requires multiplication and division by 16. Best to use a computer.