Password Entropy Calculator

Calculate the entropy and strength of passwords based on length and character sets used.

Calculate Your Password Entropy Calculator

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What is Password Entropy?

Password entropy is a measure of how unpredictable a password is. It's measured in bits and represents the amount of information or uncertainty in a password. The higher the entropy, the more secure the password is against brute-force attacks.

Password entropy is calculated using the formula: Entropy = Log₂(C^L), where C is the size of the character set (number of possible characters) and L is the length of the password.

Why Password Entropy Matters

Understanding password entropy is crucial for creating strong passwords. A password with higher entropy is more resistant to:

  • Brute-force attacks where attackers try every possible combination
  • Dictionary attacks that use common words and phrases
  • Pattern-based attacks that exploit predictable character sequences

Character Sets and Their Impact

The character sets you use in your password significantly affect entropy:

Character SetExamplesSize (Possible Characters)Bits of Entropy per Character
Lowercase letters onlya-z264.7
Uppercase letters onlyA-Z264.7
Numbers only0-9103.32
Special characters!@#$%^&*()-=_+~33~5
All of the abovea-zA-Z0-9!@#$%^&*()-=_+~95~6.6

Practical Password Strength Guidelines

Based on entropy values, here are some guidelines for password strength:

Entropy (bits)StrengthExample
<28Very WeakShort, simple passwords with predictable patterns
28-35WeakPasswords that might resist casual attackers but not dedicated ones
36-59ReasonablePasswords that require significant computational resources to crack
60-127StrongPasswords resistant to targeted attackers with significant resources
128+Very StrongPasswords likely to resist even state-sponsored attackers

Tips for Creating High-Entropy Passwords

  1. Use longer passwords (length increases entropy exponentially)
  2. Include a mix of character types (uppercase, lowercase, numbers, symbols)
  3. Avoid common words, phrases, or patterns
  4. Consider using passphrases: multiple random words with modifications
  5. Use a password manager to generate and store truly random passwords
  6. Use different passwords for different services

Password Entropy vs. Practical Security

While entropy is important, remember that real-world security involves more factors:

  • Enable two-factor authentication when available
  • Be aware of phishing and social engineering attacks
  • Update passwords regularly, especially after data breaches
  • Check if your accounts have been compromised at sites like haveibeenpwned.com

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Frequently Asked Questions

Password entropy is a measure of password strength expressed in bits, representing how unpredictable a password is. Higher entropy indicates a password that's more resistant to brute force attacks because there are more possible combinations to try.

Password entropy is calculated using the formula: Entropy = Log₂(C^L), where C is the size of the character set (number of possible characters) and L is the length of the password. For example, a password using 95 possible characters that is 12 characters long has an entropy of about 78.7 bits.

Generally, passwords with entropy above 60 bits are considered strong, while those with 80+ bits are very strong. For critical applications, 100+ bits is recommended. NIST suggests at least 70 bits of entropy for sensitive accounts.

Yes, adding special characters increases the character set size, which increases entropy. However, the benefit diminishes if you're already using a large character set. Increasing password length is generally more effective than adding more character types.

Password length typically contributes more to entropy than complexity. For example, a 16-character password using only lowercase letters (entropy ≈ 75 bits) is stronger than an 8-character password using all possible characters (entropy ≈ 52 bits). The ideal password combines both length and diverse character types.

Each bit of entropy doubles the average time needed for a brute force attack. A password with 70 bits of entropy would require 2^70 guesses on average, which is approximately 10^21 attempts - far beyond practical cracking capabilities with current technology.

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