How many hash functions does my bloom filter need?

Question

Wikipedia says:

An empty Bloom filter is a bit array of m bits, all set to 0. There must also be k different hash functions defined, each of which map

Answer 1

Given a number of bits per key you want to "invest", the best k is:

max(1, round(bitsPerKey * log(2)))

Where max is the higher of the two, round rounds to the nearest integer, log is the natural logarithm (base e).