Strength is a count of possibilities
A password is strong when an attacker would have to try an enormous number of candidates to find it. For a password generated at random, that number is easy to calculate: with an alphabet of N characters and a length of L, there are N^L possibilities. It is usually expressed in bits of entropy, L × log2(N), where each extra bit doubles the work.
The printable ASCII characters — 26 lowercase, 26 uppercase, 10 digits and 32 symbols — give N = 94, or about 6.55 bits per character. Leaving out symbols gives N = 62, about 5.95 bits. Length therefore matters more than variety: adding one character to a 94-character password adds 6.55 bits, while adding symbols to a 12-character alphanumeric password adds only about 7 bits in total.
| Random password | Bits | Average time at 10 billion guesses per second |
|---|---|---|
| 8 lowercase letters | 37.6 | about 10 seconds |
| 8 characters, all types | 52.4 | about 4 days |
| 10 letters and digits | 59.5 | about 1 year |
| 12 characters, all types | 78.7 | about 754,000 years |
| 16 characters, all types | 104.9 | far longer than the age of the universe |
Ten billion guesses per second is a realistic figure for an attacker with a stolen database of passwords stored with a fast hash and a few graphics cards. Against a website that locks the account after a handful of wrong tries, even an 8-character password would take a very long time — but you cannot know how a website stores passwords, or whether its database will leak, so plan for the offline case.
All of this applies only to passwords chosen at random. A password a person invents — a word, a capital at the start, a digit and an exclamation mark at the end — follows patterns attackers know well, and its real strength is far below what its length suggests. "Password1!" meets every old complexity rule and is among the first things any cracking tool tries.
Passphrases: long and easy to type
A passphrase is a sequence of words chosen at random from a list. The password generator uses the EFF short wordlist of 1,296 words, so each word adds log2(1296) ≈ 10.3 bits. Four words give 41.4 bits, five give 51.7, six give 62.0 and seven give 72.4. The words must be chosen by the generator, not by you: a phrase you make up, such as a song lyric, is far easier to guess.
Passphrases are best where you have to type the password yourself — the login to your computer, or the master password of a password manager. For those, six or seven words are a good choice. For everything else, a password manager can generate and remember a 16-character random password, and you never type it at all.
What current guidance says
The US National Institute of Standards and Technology publishes the digital identity guidelines that most other guidance draws on. The current revision, SP 800-63B-4, sets these requirements for services that check passwords:
- Minimum length 15 characters when a password is the only thing needed to log in; at least 8 when it is part of multi-factor authentication.
- Allow at least 64 characters, and accept spaces and all printable characters, including Unicode.
- No composition rules. Services shall not require mixtures of character types.
- No periodic changes. Services shall not force people to change passwords on a schedule — only when there is evidence the password has been compromised.
- Check against a blocklist of common, expected and previously breached passwords.
- No password hints and no knowledge-based questions such as "name of your first pet".
The reasoning behind dropping forced changes is that people who must change a password every 90 days make predictable changes — Summer2025! becomes Autumn2025! — which adds nothing against an attacker who already has the old one. Many workplaces still enforce the old rules; if yours does, a password manager makes them less painful.
The habits that matter more than the password
- Use each password in one place only. Attackers routinely try passwords leaked from one site on others. Reuse turns one leak into many break-ins, however strong the password.
- Use a password manager. It generates a unique random password for every site and fills it in only on the real site, which also protects against many phishing pages.
- Turn on multi-factor authentication for email, banking and anything that can reset other accounts. A passkey or an authenticator app is stronger than a text message code.
- Protect your email account above all. Whoever controls it can reset almost every other password you have.
- Change a password when it may have leaked, not on a timetable.
Where hashes come in
A hash function turns any input into a fixed-length fingerprint. The same input always gives the same fingerprint, and a one-character change gives a completely different one: the SHA-256 of "hello" begins 2cf24dba, while the SHA-256 of "Hello" begins 185f8db3. The hash generator on this site computes MD5, SHA-1 and the SHA-2 family for text or files.
Its everyday use is checking downloads. Many software projects publish a SHA-256 checksum next to the download link; drop the file into the hash generator, paste the published checksum, and the tool tells you whether they match. A match means the file arrived exactly as published. MD5 and SHA-1 are still fine for catching accidental corruption but are broken against deliberate tampering, so prefer SHA-256 when it is offered.
Hashes are also how well-run websites store passwords — but not these hashes. General-purpose hashes like SHA-256 are designed to be fast, which is exactly what an attacker with a stolen database wants. Password storage uses deliberately slow functions such as Argon2, scrypt or bcrypt, with a random salt per password. Do not use the hash generator to "encrypt" a password: hashing a weak password with SHA-256 does not make it strong, and a hash is not encryption, because it cannot be reversed by anyone, including you.
Randomness you can trust
The same property that makes a generated password strong — every outcome equally likely and impossible to predict — is what makes a draw fair. The password generator, the random picker and the passphrase generator all take their randomness from the browser's cryptographic random number generator, and use rejection sampling so that no outcome is even slightly more likely than another. The random picker shuffles with the Fisher–Yates method, in which each of the n! possible orders has the same probability.
For a prize draw or picking who presents first, that means the result is as fair as rolling a perfect die. What it cannot give is proof to other people that you did not simply draw again until you liked the result. For a draw that others need to trust, do it live on a shared screen, or record it.
Limits
- Crack-time figures are estimates for a single attacker speed. Real attackers vary by many orders of magnitude, and the figures assume a truly random password.
- A generated password is only as safe as where you keep it. A password written in a shared document or sent in a chat is exposed, whatever its length.
- Services set their own rules. Some still cap length or demand particular characters; the generator's options let you meet those rules.
Frequently asked questions
How long should a password be?
For a random password kept in a password manager, 16 characters is plenty. NIST SP 800-63B-4 requires a password to be at least 15 characters when it is the only login factor.
Do I need to change my passwords regularly?
No. Current NIST guidance says services should not force periodic changes. Change a password when there is reason to think it has leaked.
Is SHA-256 a good way to store passwords?
No. It is too fast. Password storage should use a slow, salted function such as Argon2, scrypt or bcrypt.