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Password strength calculator

Entropy in bits and the time to guess a password or passphrase by brute force. Nothing you type is sent: you enter only the length and character set.

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Entropy 78.8 bits

Strength

  1. Very weak (under 36 bits)
  2. Weak (36–59)
  3. Reasonable (60–79)
  4. Strong (80–127)
  5. Very strong (128+)

How it works

bits = length × log₂(characters)

Each truly random character adds log₂(pool size) bits: about 4.7 for a lowercase letter, 6.6 for any printable character. A random 4-word passphrase from the 7,776-word Diceware list has 4 × 12.9 = 51.7 bits; 6 words have 77.5. Every extra bit doubles the guessing time. This assumes random choices; real passwords made of names, dates or common words are far weaker than their length suggests.

  1. Length × log₂(characters) 12 × log₂(95) = 78.8 bits
  2. Half of 2^bits guesses, at the attacker’s speed 2^78.8 ÷ 2 ÷ 10,000,000,000 per s

Good to know

  • Use a password manager and unique passwords; length beats complexity.

Printed from rocketcalc.io/computing/password-entropy