Litecoin - how to calculate the difficulty from 2^-N In the following list I always see difficulty values like 2^-12
How to calculate the actual difficulty from it?

Comparison of mining pools
First of all, actual difficulty is defined as the number d such that the probability of a random hash being valid is 1/(d*2^32). In other words, the hash needs to have at least 32 + log_2(d) zeros in front of it to be valid. (This is not exactly the case if d is not a power of 2, but you get the general idea.)

In that article, a difficulty of 2^-12 means that the probability of a random share being valid is 1/(2^-12 * 2^32) = 2^-20. Note that typically, pool difficulty, is measured in multiples of 2^-16 for reasons discussed in the article, so a difficulty of 2^-12 would be a pool difficulty of 2^4 = 16.