Password Generator and Password Entropy Calculator
Generate passwords, passphrases and PINs from your browser’s cryptographic random source, with entropy counted exactly, even under site rules. Check any password’s ceiling in bits and the patterns that lower it, against three named attack models and NIST’s length rule. Nothing leaves the page.
Press Generate. The entropy panel updates as you change settings, so you can see what an option costs before you use it.
Each time assumes the attacker knows exactly how the password was made: the set, the length, the wordlist. That makes it a floor, not a hope. Expected work is half the keyspace, 2^(bits − 1) guesses.
What this password entropy calculator does differently
The brand-name generators we reviewed show a strength label or bar rather than bits; the smaller tools that do show bits work them out from the full character set. This one shows the bits and the working that produced them. The interesting case is a rule such as use at least one of each character type: none of the tools we reviewed shows how such a rule changes the count. Here the rule is counted exactly, so the figure goes down when you add one, which is the direction it really moves.
| Typical generators | This tool | |
|---|---|---|
| Randomness | Named by some (Nayuki, randomkeygen), not by others | crypto.getRandomValues, with rejection sampling so no character is favoured |
| Strength shown as | A label or bar (Bitwarden, 1Password, RoboForm); bits on some smaller tools | Bits, with the formula and every step printed |
| Required character types | Not counted separately by any tool we reviewed | Counted exactly by inclusion-exclusion |
| Crack time | Where shown, one attack rate | Three named attack models, each rate printed |
| Passphrases | Some name their list (TrustComponent uses the EFF list) | The tool’s own 2,430-word list, 11.2467 bits a word, with its properties stated |
| Checking a password you have | Bits from the character types used (Omni Calculator) | A ceiling in bits, the patterns that lower it, and the NIST length check |
| Site rules | Some options, such as excluding similar characters | Custom symbol set, excluded characters, start with a letter, all counted |
Generators reviewed in October 2026: Bitwarden, 1Password, RoboForm, randomkeygen, Omni Calculator, TrustComponent and Nayuki.
How password entropy is calculated
For a password picked at random, entropy is the base-2 logarithm of the number of passwords the method could have produced: E = L × log2(N), where L is the length and N the number of characters in the set. A 16-character password over the 86 characters this tool uses by default is 16 × log2(86) = 102.8 bits. Each extra bit doubles the number of guesses an attacker needs.
Rules change the count. Requiring at least one lowercase letter, capital, digit and symbol removes every password that lacks one of them. The tool counts what is left by inclusion and exclusion: all passwords, minus those missing each type, plus those missing each pair, and so on. At 8 characters the rule costs about one bit (51.4 falls to 50.4); at 20 characters it costs a tiny fraction of one. Start with a letter is counted the same way. Dropping look-alike characters or excluding a symbol shrinks N, and the figure follows.
All of this assumes the password was generated at random. For a password a person chose, the formula gives a ceiling, not an estimate: Summer2024! uses four character types and 11 characters, so the formula says about 72 bits, but it is a word, a year and a symbol in the most common order, and guessing software tries that shape early. That is why the calculator lists the patterns it finds and labels its number a ceiling.
How many bits of entropy is a strong password?
It depends on how the password can be attacked, so the tool shows three cases side by side rather than one crack time. Each assumes the attacker knows exactly how the password was made, and expected work is half the keyspace.
| Bits | Behind a throttled login (10 guesses a second) | Offline, slow hash (10,000 a second) | Offline, fast hash on GPUs (10^12 a second) |
|---|---|---|---|
| 40 | about 1,700 years | about 1.7 years | under a second |
| 60 | about 1.8 billion years | about 1.8 million years | about 7 days |
| 80 | far beyond | about 1.9 trillion years | about 19,000 years |
| 100 | far beyond | far beyond | about 20 billion years |
Times are 2^(bits − 1) guesses divided by the rate. The rates are assumptions, printed so you can disagree with them.
The useful reading: a password a password manager stores for you should be long enough that the fast-hash column does not matter, which at 102.8 bits a 16-character random password already is. A password you must type from memory has to survive an offline attack only if a site loses its database, and for that the slow-hash column is the honest one, since NIST SP 800-63B-4 requires services to salt passwords and hash them with a password hashing scheme that takes a cost factor, which is what makes guessing slow.
Passphrase or password, and how many words
A passphrase is a few words picked at random. Each word from this tool’s 2,430-word list adds 11.2467 bits, so six words is 67.5 bits and seven is 78.7. A 12-character random password over the full set is 77.1 bits, so the password is stronger per character and a six-word passphrase is not stronger than it. What a passphrase wins on is being typable from memory without mistakes, which matters for the few passwords you actually type: the password manager, a laptop, a disk.
The EFF large wordlist has 7,776 words, about 12.9 bits a word, and six of its words give about 77 bits. This tool’s list is shorter because every word is 3 to 8 letters, spell-checked, with common homophone pairs such as steal and steel removed, and identified by its first four letters, so seven of its words match six of the EFF’s. For Diceware, its creator Arnold Reinhold has recommended at least six words since 2014. Capitalising every word adds nothing because it is predictable; capitalising words at random adds one bit a word, and the tool counts both correctly.
What NIST SP 800-63B-4 says about passwords
The US National Institute of Standards and Technology published the final version of NIST SP 800-63B-4 on 31 July 2025. Its password rules, for services that check passwords, are worth knowing because sites increasingly follow them:
- A password used on its own must be at least 15 characters; one used as part of multi-factor authentication can be as short as 8.
- Services should allow passwords of at least 64 characters.
- Services shall not impose other composition rules, such as requiring a mix of character types.
- Services shall not require periodic changes, but must force a change if there is evidence of compromise.
- New passwords must be compared against a blocklist of common, expected or compromised values.
- Services shall allow password managers and autofill, and should permit pasting.
The entropy calculator checks the length rule for any password you type. It cannot check a blocklist, because doing that properly means sending something about the password to a service that holds one, and this page sends nothing.
What this page does not do
The generator makes no network request with anything you type or generate, writes nothing to local storage or a cookie, and sends no analytics event carrying a value. You can confirm that in your browser’s network panel. A generated password is only as safe as where it goes next: copying puts it on the system clipboard, which other apps can read and some systems sync, so paste it into a password manager and move on. The .txt download exists for setting up several accounts at once; delete the file when you are done.
For the other tools on this site, which are about search rather than security, start with the tools hub.