Password Entropy Calculator – Bits of Entropy
Calculate the entropy (randomness) of a password in bits.
About This Calculator
Calculate the entropy (randomness) of a password in bits. Use the calculator above for instant results.
Worked Examples
- 16 × log2(95) = 16 × 6.57 = 105.1 bits | Extremely strong
Answer: 105.1 bits — extremely strong
- 8 × log2(62) = 8 × 5.95 = 47.6 bits | Moderate
Answer: 47.6 bits — moderate
- 20 × 6.57 = 131.4 bits | Overkill for most uses
Answer: 131.4 bits — overkill
Who Uses This Calculator?
Measure password strength quantitatively.
Set entropy-based password policies.
NIST password compliance.
Teach entropy and password strength.
Common Mistakes to Avoid
❌ Entropy assumes random generation
These calculations assume each character is randomly chosen. A predictable password like 'Password1!' has much lower effective entropy despite meeting 'complexity requirements'.
❌ Dictionary words reduce entropy
Using actual words gives roughly 11 bits per word (English has ~2,048 common words). 4 random words ≈ 44 bits.
Frequently Asked Questions
What entropy is sufficient?
NIST recommends minimum 80 bits for sensitive accounts. 40 bits for low-value accounts. 128+ bits for long-lived master passwords.
Entropy vs password policies?
Typical 'strong password' requirements (8 chars, upper+lower+number+symbol) give ~52 bits. A random 16-char alphanumeric gives 95 bits — twice as good.
Passphrase entropy?
4 words from 2,048-word list: 4 × 11 = 44 bits. 6 words: 66 bits. Memorable and strong. Method: Diceware.