I assume you are thinking of binary rather than hexadecimal? Binary is base 2 (hence either 0 or 1s) where as Hexadecimal is base 16.
Assuming you are talking about binary:
- If you have 8 bits you have 28 possibilities.
- If you have 9 bits you have 29 possibilities.
- If you have 10 bits you have 210 possibilities.
Etc…
You can therefore use the PHP pow function:
$possibilities = pow(2, 10);
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solved How many possibilities on a binary? [closed]