32 bits, one for the sign, 31 bits of information:
2^31 - 1 = 2147483647
Why -1?
Because the first is zero, so the greatest is the count minus one.
EDIT for cantfindaname88
The count is 2^31 but the greatest can't be 2147483648 (2^31) because we count from 0, not 1.
Rank 1 2 3 4 5 6 ... 2147483648
Number 0 1 2 3 4 5 ... 2147483647
Another explanation with only 3 bits : 1 for the sign, 2 for the information
2^2 - 1 = 3
Below all the possible values with 3 bits: (2^3 = 8 values)
1: 100 ==> -4
2: 101 ==> -3
3: 110 ==> -2
4: 111 ==> -1
5: 000 ==> 0
6: 001 ==> 1
7: 010 ==> 2
8: 011 ==> 3
