Password Entropy Calculator
Calculate the entropy (bits of randomness) and estimated crack time of any password based on its character set and length.
Analyzed entirely in your browser — never sent to any server.
About Password Entropy Calculator
Password entropy measures unpredictability, in bits: each extra bit doubles the number of attempts an attacker needs. The textbook formula is length × log₂(charsetSize), and it is exactly right for a password a machine generated at random — but badly wrong for one a human chose. It has no way to know that Password1! is a top-ranked breach password wearing a digit and a symbol, so it awards it about 66 bits: more than a random 9-character string, and utterly wrong.
This calculator reports effective entropy instead. It searches for the cheapest description of your password out of common passwords, dictionary words, names, keyboard runs, sequences, repeated blocks, dates and letter-for-symbol substitutions, and brute-force arithmetic covers only what is left over. The bits you see are the base-2 logarithm of that guess count, so they are directly comparable across passwords — and the four attack scenarios show why the same number means "safe" behind a rate-limited login form and "already cracked" in a leaked hash dump. Because the built-in word lists are compact, an unusual word may still be treated as random, so read the figure as an upper bound.
Private & free — this tool runs entirely in your browser.