Calculate password entropy

Estimate the theoretical entropy of a password in bits.

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ToolPassword Entropy Calculator
Input
Output
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How it works

Estimated entropy is the base-2 logarithm of the number of possible guesses: for uniform random characters it is length multiplied by log2 of the alphabet size. Human-chosen passwords do not follow that uniform model, so the estimate is an upper bound rather than a crack-time guarantee.

  • Bits provide a common logarithmic scale for comparing search spaces.

Worked example

Calculate Entropy
Measure the entropy of a password to assess its strength
Input
											MyP@ssw0rd!2024
Output
												=== Password Entropy Analysis ===

Password length: 15 characters
Unique characters: 12
Character pool size: 95

Standard entropy: 98.55 bits
Shannon entropy: 52.60 bits
Bits per character: 6.57

Security level: Very Good (strong)
Key equivalent: DES-equivalent or weaker

Character classes used:
  Lowercase (a-z): Yes (+26)
  Uppercase (A-Z): Yes (+26)
  Digits (0-9): Yes (+10)
  Symbols: Yes (+33)
  Spaces: No
  Unicode: No

Entropy thresholds:
  28 bits  = Weak       [PASS]
  40 bits  = Fair       [PASS]
  60 bits  = Good       [PASS]
  80 bits  = Strong     [PASS]
  128 bits = Excellent  [FAIL]

When to use this

Password policies, security reviews, and manager explanations compare secret strength.

Edge cases

  • A repeated character has far less entropy than a random string of the same length.
  • A dictionary phrase violates the uniform-alphabet assumption.
  • Adding a symbol that users always append adds little uncertainty.

References