Binary numbers are a way of representing numbers using only two digits: 0 and 1. Each digit in a binary number is called a bit, and the value of each bit is determined by its position in the number. The rightmost bit represents 2^0 (1), the next bit to the left represents 2^1 (2), then 2^2 (4), and so on.
The easiest way to convert a binary number to a number, is starting at the right-most value, and then moving to the left. So from right to left on a 8-bit binary number 00000000, the values are 1, 2, 4, 8, 16, 32, 64, and 128.
0
0
0
0
0
0
0
0
128
64
32
16
8
4
2
1
Because of that, given an 8-bit binary number, the maximum value of it can only ever be 255.
This is because given a binary number that's 11111111, this is how it's structured:
1
1
1
1
1
1
1
1
128
64
32
16
8
4
2
1