There'll actually be 256 combinations. The maximum value
that can be represented with a byte (8 - bits) is 255 but as
far as combinations are concerned 0 should also be
considered as well as 1, 2, 3, ..., 255. So there are total
256 combinations.

256 combinations.Byte contains the 8 Bits and bit contains
either the value 0 or 1.i.e.(2 raise to power 8 minus
1).The maximum number of value represented with a byte is 8
bits is 255 but 0 should also be considered as well as 1,
2, 3, ..., 255. So there are total
256 combinations.

if number of bite values is n, and length of the byte is k.
that means n = 2, k = 8.
for n even => n^k
(2^8 = 256)
for n odd => n^k - 1
(2^7 - 1 = 128-1 = 127)