How is password entropy calculated?

Entropy (bits) = log2(character set size) × password length. A 12-character password using lowercase only has log2(26)×12 = 56.5 bits. Adding uppercase + numbers boosts it to 71.5 bits.

How many entropy bits make a password secure?

Under 40 bits: very weak. 40–60 bits: moderate. 60–80 bits: strong. Over 80 bits: very strong. A 4-word passphrase from a 7,776-word list has 51.7 bits per word × 4 = excellent security.

Password Strength & Entropy Bits Calculator

Calculate the entropy in bits and estimated crack time for any password. See how length, character sets, and randomness affect the time needed to brute-force your password.

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Enter the values for the scenario you are assessing. Calculate the entropy in bits and estimated crack time for any password. See how length, character sets, and randomness affect the time needed to brute-force your password. Use the password entropy result to inform your calculation.

Password Strength & Entropy Bits Calculator

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Frequently Asked Questions

How is password entropy calculated?

How many entropy bits make a password secure?