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What Makes a Password Strong? Entropy Explained Simply

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“Use a capital letter and a symbol” is outdated advice. What really matters is how unpredictable a password is — measured in bits of entropy.

Entropy in one formula

For a truly random password, entropy = length × log₂(number of possible characters). A 16-character password using all 94 printable characters has about 105 bits of entropy.

How many bits are enough?

  • Under 50 bits: weak.
  • 72+ bits: strong.
  • 100+ bits: very strong — ideal for master passwords.

Generate, don’t invent

Humans are terrible at randomness. Use the Random Password Generator, which runs locally in your browser with cryptographic randomness, and store the result in a password manager.

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