Password Entropy Calculator
Measure password strength in bits of entropy and see how long an offline attack would take at realistic cracking rates.
Your details
Attack model
Determines guesses per second an attacker achieves offline
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
Entropy
78.7 bits
Strong — about 377.3 billion years to crack against bcrypt at a sensible work factor
Includes your inputs, the full breakdown, and every row of the table.
Verdict
Strong
Possible combinations
10^23.7
Average time to crack
377.3 billion years
Attacker rate assumed
20,000/sec
- Length
- 12 characters
- Character set size
- 94
- Entropy per character
- 6.55 bits
- Total entropy
- 78.7 bits
| Stored as | Guesses/sec | Average crack time |
|---|---|---|
| Unsalted MD5 on a GPU rig | 1,000,000,000,000 | 7,546 years |
| Single-round SHA-256 on a GPU rig | 10,000,000,000 | 754,567 years |
| bcrypt at a sensible work factor | 20,000 | 377.3 billion years |
What this means
- This assumes a genuinely random password. If you chose it yourself, real entropy is far lower — attackers try dictionary words, substitutions and known breach lists long before brute force.
- A five-word random passphrase from a large word list carries roughly 64 bits, beats most twelve-character passwords, and is vastly easier to type.
- Entropy is irrelevant if the password is reused. Credential stuffing tries known pairs directly and never has to guess at all.
How the password entropy calculation works
Entropy measures how many guesses an attacker must make on average, expressed in bits so the numbers stay manageable. Each additional bit doubles the work. The calculation is simply length multiplied by the base-two logarithm of the character set, which is why length beats complexity: adding one character to a password multiplies the search space by the whole alphabet, while adding a symbol to a short password barely moves it.
The crack time depends far more on how the password is stored than on the password itself. A properly hashed password using bcrypt or Argon2 limits an attacker to tens of thousands of guesses per second, because the algorithm is deliberately slow. The same password stored as an unsalted MD5 hash can be attacked at a trillion guesses a second on commodity hardware. That is a difference of roughly eight orders of magnitude, and it is entirely outside the user's control.
Frequently asked questions
How many bits of entropy is enough?
For an account protected by a service that hashes properly and rate-limits login attempts, anything above about 60 bits is comfortable. For a password guarding an encrypted file or a password manager vault, where an attacker can grind offline without limit, aim for 100 bits or more. Below 40 bits is not meaningfully protective against a determined attacker.
Is a passphrase really better than a complex password?
Usually, yes. Five words drawn randomly from a list of around eight thousand gives roughly 64 bits, which exceeds a typical twelve-character mixed password — and it is far easier to remember and type. The critical word is randomly: a memorable phrase you invented has almost no entropy, because attackers use exactly those patterns.
Does this reflect real-world attacks?
Only for random passwords. Real attackers never brute-force blindly. They start with breach corpora, dictionary words, keyboard patterns and predictable substitutions like replacing letters with digits, so human-chosen passwords fall dramatically faster than their nominal entropy suggests. Treat this figure as an upper bound on your strength, not an estimate of it.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.