Password Entropy Calculator

What is password entropy?

Entropy is a measure of how unpredictable a password is, expressed in bits. Each additional bit doubles the number of guesses an attacker must make, so entropy is the single best mathematical gauge of password strength. This free password entropy calculator estimates entropy from your password's length and the size of its character set (lowercase adds 26 possibilities per position, uppercase another 26, digits 10, symbols about 33), then shows the full "keyspace" — the total number of possible combinations — and how long that would take to crack under three realistic attack speeds.

The three scenarios matter because not all attacks are equal. An online attack against a login form is slow (throttling and lockouts). An offline attack on a fast-hashed leaked database can try billions per second, while a properly slow-hashed database (bcrypt, Argon2) drops that to thousands. As a benchmark, aim for 70+ bits of entropy for important accounts and 100+ for anything critical. Note that dictionary words and predictable patterns lower real-world strength below the raw math, so favor random passwords or passphrases. Everything is calculated locally in your browser and never sent anywhere.