Password Entropy Calculator
Measure password strength the way security engineers do — in bits of entropy. See the classic formula (length × log2 of the character pool), a realistic estimate that accounts for words, dates and patterns, and what those bits mean in time to crack.
Entropy (bits) = length × log2(pool size), where the pool is the number of possible characters: 26 for lowercase, 62 for letters and digits, 95 for all printable ASCII. That formula is only accurate for randomly generated passwords; for human-chosen ones this calculator also gives a realistic estimate that discounts dictionary words, sequences and dates.
Checked in your browser. The password is never sent anywhere; the optional breach check sends only the first 5 characters of its SHA-1 hash (k-anonymity).
Entropy of randomly generated passwords
| Character set | 8 chars/words | 12 chars/words | 16 chars/words | 20 chars/words |
|---|---|---|---|---|
| Digits only (0–9) (10) | 27 bits | 40 bits | 53 bits | 66 bits |
| Lowercase (a–z) (26) | 38 bits | 56 bits | 75 bits | 94 bits |
| Letters (a–z, A–Z) (52) | 46 bits | 68 bits | 91 bits | 114 bits |
| Letters + digits (62) | 48 bits | 71 bits | 95 bits | 119 bits |
| All printable ASCII (95) | 53 bits | 79 bits | 105 bits | 131 bits |
| Diceware word (EFF list) (7776) | 103 bits | 155 bits | 207 bits | 258 bits |
Entropy (bits) = length × log2(pool size). Each extra bit doubles the guesses needed. 60–80+ bits is strong for online accounts; use 80+ for encryption keys and master passwords.
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How to use Password Entropy Calculator
- 1Type a password or passphrase.
- 2Compare the naive entropy with the realistic estimate.
- 3Check the crack times for each attack scenario.
- 4Use the reference table to pick a length for generated passwords.
The entropy formula
For a password generated uniformly at random, entropy H = L × log2(N), where L is the length and N the number of possible symbols. A random 12-character password from 62 alphanumerics has 12 × 5.95 ≈ 71 bits. Each bit doubles the attacker's work, so 80 bits is a thousand times harder than 70.
Diceware passphrases use the same maths with words: each word from a 7,776-word list adds log2(7776) ≈ 12.9 bits.
Why human passwords have less
“Summer2024!” scores about 72 bits by the naive formula, but an attacker tries season-plus-year patterns early, so its real entropy is closer to 20 bits. That's why this calculator shows both. For guaranteed entropy, generate passwords with the Strong Password Generator.
Frequently Asked Questions
How many bits of entropy is a strong password?
Roughly: under 40 bits is weak, 60 bits is reasonable for online accounts protected by rate limiting, and 80+ bits is strong enough for master passwords and encryption keys.
Does a longer password always have more entropy?
Only if the extra characters are unpredictable. Repeating a word or adding “123” adds length but very little entropy.
Is my data sent to your server?
No. This tool runs entirely in your browser using the Web Crypto API and JavaScript. Nothing you type or generate is uploaded, logged or stored.
Guides & Tutorials
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