Password Entropy

Password entropy predicts how difficult it is to crack a given password via brute force, dictionary attacks or other methods. Entropy is essentially shows how many guesses an attacker will need to crack your password. The higher the entropy, the more difficult it is to crack. A password entropy of at least 75 bits and above is considered very strong.

e = log2(R^L)
_{e = entropy
R = range of characters
L = length of password}