Password Entropy Calculator
Calculate the entropy of a password in bits and see how long an offline attack would take at realistic cracking rates.
Runs entirely in your browser. Your input is never sent to our servers.
What is Password Entropy?
Password entropy is a measure, in bits, of how many equally likely possibilities a password was drawn from — a property of the process that generated it, not of the characters it happens to contain.
What this Password Entropy Calculator does
This calculator reports the size of the character set a password draws on, the entropy that implies for its length, the resulting search space, and how long an offline attack against a fast hash would take to work through it.
It reports that figure as a ceiling, and says so on every result. The arithmetic assumes each character was chosen uniformly at random. For a password a person invented, the real entropy is far lower, because an attacker does not enumerate the character space — they try words, names, dates, keyboard runs and substitutions first.
How to use it
- Type or paste the password. It stays in your browser; no request is made.
- Read the entropy in bits and the estimated offline crack time.
- Treat the number as an upper bound. If you chose the password yourself, assume materially less.
Understanding your results
Entropy ceiling — length multiplied by the log base two of the character set size. Adding one character to a 94-symbol set adds about 6.6 bits; adding a symbol type to an existing length adds far less.
Offline crack time — assumes 1011 guesses per second against a fast hash such as SHA-256, and that the answer is found halfway through the space. Against Argon2id or bcrypt it would be enormously longer; against a password already exposed in a breach, instant.
Verdict — roughly: below 60 bits is weak, 60–90 is adequate only where online rate limiting applies, above 90 is sound against offline attack.
Why this matters
Length dominates. Every additional character multiplies the search space, while adding a symbol to a short password merely widens the alphabet a little. That is why a long passphrase of ordinary words beats a short string of punctuation, and why composition rules that force a symbol and a digit produce predictable passwords without adding much real strength.
Current NIST guidance reflects this: favour length, screen candidates against known breached passwords, and drop mandatory periodic rotation, which pushes people toward small predictable variations of a password they already use.
Common mistakes
Reading the figure as a score for a human-chosen password. It is the strength of random generation at that length and alphabet, which is not the same thing.
Substituting characters to look stronger. P@ssw0rd! gains almost nothing: every cracking tool tries those substitutions as a matter of course.
Assuming entropy protects a reused password. If it appears in a breach corpus, its entropy is irrelevant — it is tried directly.
Limitations
This does not check the password against breach corpora, dictionaries or common-password lists, and it does not model the ordering a real cracker would use. It measures the space, not the likelihood of a particular guess arriving early in it.
The crack-time figure moves with hardware and with the storage function in use. Treat it as an order of magnitude, not a prediction.
Frequently asked questions
How many bits of entropy is enough?
For a password protecting something that matters and may be attacked offline, aim above 90 bits. Between 60 and 90 is only adequate where an attacker is limited to online attempts against a rate-limited service.
Is a passphrase better than a complex short password?
Usually, because length contributes more than alphabet size. Four or five genuinely random words drawn from a large list comfortably exceeds a short string of mixed symbols, and is far easier to remember and type.
Why does this tool say the number is a ceiling?
Because the formula assumes uniform random generation. A password a person chose sits in a much smaller effective space, and a cracker searches that smaller space first. Reporting the ceiling as a score would flatter weak passwords.
Should passwords be changed regularly?
NIST SP 800-63B advises against forced periodic rotation. It drives predictable incremental changes. Change a password when there is evidence of compromise.
References
Last reviewed