Password Entropy Calculator

Entropy is the length times log₂ of the character pool: twelve characters from the 95 printable ASCII symbols carry 78.84 bits. Every extra bit doubles the guesses an attacker needs. The figure only holds for a password a machine picked at random — a word you chose yourself is worth far less.

Entropy measures the size of the space a password was drawn from, counted in bits. When every position is filled independently from a pool of N symbols, there are N to the power of L possible passwords, and the entropy is the base-2 logarithm of that count: H = log₂(N^L) = L × log₂(N). A bit is one yes-or-no question, so the figure says how many such questions stand between an attacker and the right string. The default settings run through it directly: each of the 95 printable ASCII symbols carries log₂(95) ≈ 6.5699 bits, and twelve independent draws carry twelve times that, 78.8383 bits. What the number does not give is a time. How long a search takes depends on how fast the attacker can guess and on what they are guessing against, and none of that appears in the formula. It also names no threshold — the strength bands that circulate for figures like these are not carried by the source cited here, so this page declares no bit count sufficient. The limitation that matters most is that entropy describes the procedure, not the characters. It is a property of how the password was chosen, which is why the same twelve characters can be worth 78.8383 bits or far less.