What Is Password Entropy?
Password entropy is a measure of how unpredictable a password is, expressed in bits. For a randomly generated password, entropy = length × log2(number of possible characters). Each extra bit doubles the number of guesses needed in a brute-force attack, so longer random passwords are much stronger.
Example
A random 12-character password using 94 printable characters has about 12 × 6.55 ≈ 79 bits of entropy.
Limitations
The formula assumes true randomness. Passwords based on words, names, or patterns are far easier to guess than their length suggests.
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Last updated: September 27, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.