Password Entropy Calculator
Check your password strength and entropy in bits, plus estimated crack time, free in your browser with this password entropy calculator.
Enter Values
How to use this calculator
- Enter the password length and the size of the character pool.
- Press Calculate for the entropy in bits and a strength rating.
How it works
Entropy measures how hard a password is to guess: bits = length × log₂(pool size). A bigger pool (adding digits and symbols) and more length both raise it.
As a rough guide: under 40 bits is weak, 60–80 is strong, and 80+ is very strong.
Worked example
12 characters from a 95-character pool. 12 × log₂(95) ≈ 78.8 bits — strong.
Common mistakes
- Counting length only — a long password from a small character set is weaker than it looks.
- Treating predictable substitutions like P@ssw0rd as strong; cracking tools expect them.
Frequently asked questions
What is password entropy?
A measure of unpredictability in bits: entropy = length × log2(character-set size). More bits means exponentially more guesses to crack.
How many bits of entropy is secure?
Around 70–80 bits resists offline attacks for most purposes; a long random passphrase reaches this more comfortably than a short complex one.
What pool size should I use?
26 for lowercase only, 52 for mixed case, 62 with digits, and about 95 with symbols.
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Cite this tool
Zerdly. (2026). Password Entropy Calculator. Retrieved from https://www.zerdly.com/tools/password-entropy-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.