Password Entropy Calculator
Estimate a password's entropy in bits based on its length and character set, with a plain-English strength interpretation.
Type or paste a password below - this tool estimates its entropy in bits based on length and character variety, entirely in your browser.
This is calculated entirely in your browser - nothing you type here is sent to or stored on any server.
Entropy is a mathematical estimate based on character-set size, not a guarantee against real-world attacks like credential stuffing or phishing - a password can have decent entropy and still be compromised if reused elsewhere.
What Is Password Entropy?
Entropy estimates how many guesses an attacker would need in the worst case, expressed in bits - it depends on the password's length and how large a character-set pool it appears to draw from (lowercase only, mixed case, numbers, symbols).
Why Use This Tool?
Entropy gives a rough, mathematically grounded sense of a password's resistance to brute-force guessing, which is a more meaningful measure than the vague 'strength meter' colors some sites show.
How to Use It
- Type or paste a password (nothing is transmitted anywhere).
- Review the estimated bits of entropy and its strength interpretation.
Limitations
This estimate assumes the password looks randomly drawn from its apparent character set - it can't detect that "P@ssw0rd123" is a common, easily-guessed pattern despite technically containing all four character types, since that requires pattern/dictionary analysis, not pure entropy math.