Password Entropy Explained: How Strong Is Your Password?
Understand password entropy: the math behind password strength, bits of entropy calculation, and why length beats complexity.
What Is Entropy?
Password entropy measures randomness in bits. Higher entropy = harder to crack. Formula: E = L × log2(R) where L is length and R is the character set size.
Character Set Sizes
- Lowercase only (a-z): 26 characters → 4.7 bits/char
- + Uppercase (A-Z): 52 → 5.7 bits/char
- + Digits (0-9): 62 → 5.95 bits/char
- + Symbols: 94 → 6.55 bits/char
Entropy Targets
- <40 bits: Very weak (crackable in seconds)
- 40-60 bits: Weak (crackable in hours to days)
- 60-80 bits: Moderate (years with consumer hardware)
- 80-100 bits: Strong (centuries)
- 100+ bits: Very strong (heat death of universe)
Check your password: Password Strength Checker
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