Hamming code parity bits calculation
Hamming code is simply 2 or more parity bits over different groupings of data bits such that if you draw a venn diagram of each grouping you will find each data bit belongs to a unique group of parity bits.  In this way you can identify any 1 bit in error. Therefore any 1 bit error is correctable.

By definition of the Hamming code, the parity bit positions are in locations 2 to the zero through Nth power.  So the parity bits occupy the 1st, 2nd, 4th, 8th... positions.  

Example:

position:  1  2  3  4  5  6  7  8...
bit type: P1 P2 D1 P3 D2 D3 D4 P4...


The 1st data bit occupies the 3rd position.  So, if we follow the definition, 1 data bit needs 2 parity bits.  Not really worth it.  We can place the next data bit into the 5th position. So 2 data bits needs 3 parity bits.  Still not really worth it.  (In both these cases we can simply send 1 parity bit with every data bit giving the receiver the ability to detect and correct errors.)  We can place the next data bit into the 6th position.  So 3 data bits needs only 3 parity bits.  We are at the break even point with respect to sending out 1 parity bit for each data bit.  We can place the next data bit into the 7th position.  So 4 data bits needs only 3 parity bits.  Not until we get to 4 data bits do we see an advantage to using the Hamming code.  

So, as you build the Hamming code sequence (given the left to right sequence in the above example), you need all the parity bits to the left of the required number of data bits.  

I'll leave it up to you to come up with an equation to calculate the number of necessary parity bits.