MATH · PASSWORD STRENGTH ESTIMATOR — CHECK HOW STRONG YOUR PASSWORD IS
Password Strength Estimator — Check How Strong Your Password Is
Estimate the strength of a password using Shannon entropy and pattern analysis. See entropy bits, character class coverage, pattern deductions, and a strength tier — all calculated locally, never sent to a server.
About This Calculator
A strong password is your first line of defense against unauthorized access. This tool estimates password strength using Shannon entropy — a mathematical measure of unpredictability — plus heuristic deductions for common patterns (keyboard sequences, all-same characters, digits-only). Everything is calculated locally in your browser; the password is never transmitted.
How It Works
Enter a candidate password (not one you currently use) to see its entropy in bits, the character classes it uses, any pattern deductions that reduce effective entropy, and a strength tier from Very Weak to Very Strong. Higher entropy = harder to crack.
The Formula
entropy = log₂(poolSize) × length
- poolSize
- Sum of character class sizes present: a-z=26, A-Z=26, 0-9=10, symbols=32
- length
- Number of characters in the password
Frequently Asked Questions
- Is this safe to use? Can anyone see my password?
- Yes — this calculator runs entirely in your browser. The password you type is never sent to any server. However, do not enter passwords you are currently using: only test candidate passwords you are considering.
- What does entropy mean for passwords?
- Entropy (measured in bits) represents the theoretical difficulty of guessing a password by brute force. Each bit doubles the number of guesses needed. A 40-bit password requires ~1 trillion guesses; a 60-bit password requires ~1 quadrillion. Modern cracking hardware can try billions of guesses per second.
- Why does this give a different result than zxcvbn or other tools?
- Production password checkers like zxcvbn use large offline dictionaries of common passwords and patterns. This calculator uses only math-computable heuristics (character pool + pattern deductions). It will overestimate strength for common dictionary words like "password123" or "sunshine". Always use a dictionary-aware checker or a password manager for production use.
- What makes a password strong?
- Length is the single biggest factor — each extra character multiplies the guessing space by the pool size. Beyond that: use all four character classes (lowercase + uppercase + digits + symbols), avoid keyboard patterns (qwerty, 12345, asdf), avoid repeating characters, and avoid common words or names.
- Should I use this tool for real passwords?
- Use it only to test candidate passwords you are considering. For your actual passwords, use a reputable password manager (Bitwarden, 1Password, etc.) which generates cryptographically random passwords of optimal length.