Password Entropy Calculator
Calculate the precise mathematical entropy of a password in bits using the Shannon formula
H = L × log₂(N). See a complete breakdown of the character pool,
the full formula with your values substituted in, and how many guesses are required
to crack it at various attack speeds.
H = L × log₂(N) gives the theoretical maximum entropy in bits.
Common pool sizes: lowercase only = 26, lowercase + uppercase = 52, + digits = 62, + symbols = 94.
Entropy measures the unpredictability of a password in bits. Each additional bit doubles the number of guesses required to crack it by brute force.
The formula H = L × log₂(N) calculates theoretical maximum entropy, where L is the length and N is the pool of possible characters. A password of length 12 using all 94 printable ASCII characters has 12 × log₂(94) = 78.7 bits.
This is theoretical entropy — the real effective entropy may be lower if the password follows a predictable pattern (dictionary word, date, keyboard walk). The Password Strength Checker accounts for patterns; this tool shows the mathematical maximum.
| Entropy Range | Strength | Recommendation |
|---|---|---|
| < 28 bits | Very Weak | Cracked in seconds by any modern attack |
| 28 – 35 bits | Weak | Vulnerable to offline attacks within hours |
| 36 – 59 bits | Fair | Acceptable for low-value accounts only |
| 60 – 79 bits | Strong | Good for most personal accounts |
| 80 – 99 bits | Very Strong | Resistant to all practical attacks |
| 100+ bits | Excellent | Unbreakable for any foreseeable attack |