How to Create a Strong Password (NIST 2025 Rules and Entropy Table)

A strong password is long, random and used for only one account. For most accounts that means 16 or more random characters from a generator, saved in a password manager. For the few passwords you must type from memory, such as the password manager itself or your laptop login, use a passphrase of five or six randomly chosen words. Then turn on two-factor authentication or passkeys, because even a perfect password can't protect you from a fake login page or a leak.

The free password generator makes 16-character random passwords in your browser. This guide covers how passwords actually get cracked, what NIST changed in its 2025 guidance, an entropy table that shows why length wins, and exactly what the site's password tools do.

How passwords actually get cracked

• Reuse after a breach. When a website is breached, lists of email addresses and passwords circulate. Attackers try the same pairs on email, banking and shopping sites, which is called credential stuffing. If you reuse a password, its strength doesn't matter: it is already known.
• Guessable patterns. Cracking software doesn't start with random strings. It tries common passwords, names, dates, keyboard runs such as qwerty and 123456, and the usual decorations: a capital first letter, an @ in the middle, a year or 123 at the end. "Rahul@1995" ticks every "capital, symbol, number" box and follows exactly that pattern.
• Offline cracking. If a site stored passwords with a weak hash and the file leaks, attackers can test guesses on their own hardware at enormous speed, with no lock-out after wrong attempts. This is where length and randomness decide everything.
• Phishing and malware. A fake login page or a keylogger captures your password as you type it, however strong it is. Only two-factor authentication, passkeys and care with links protect you here.

What NIST's 2025 password rules say

The US National Institute of Standards and Technology (NIST) published the final version of its Digital Identity Guidelines, SP 800-63B-4, in July 2025. It is written for organisations that run logins, but it is the clearest summary of current thinking. For password systems it says:

• A password that is the only way to log in must be at least 15 characters; one used together with a second factor must be at least 8.
• Systems should allow passwords of at least 64 characters, accept spaces and all printable characters, and accept Unicode.
• Systems must not impose composition rules such as "must contain a number and a symbol".
• Systems must not force periodic changes, but must force a change when there is evidence the password has been compromised.
• New passwords must be checked against a blocklist of common, expected and breached passwords.
• No password hints visible to other people, and no security questions.
• Password managers and autofill must be allowed, and pasting a password should be allowed.

For you, that means length matters more than symbols, you don't need to change a good password every 90 days, and you should change it immediately if a site reports a breach. If a site still demands symbols or regular changes, follow its rules, but keep the length as well.

Length versus complexity: the entropy table

For a password chosen at random, strength is measured in bits of entropy: log2(charset^length), which is the same as length × log2(charset size). Each extra bit doubles the number of guesses an attacker needs. Adding one character multiplies the possibilities by the whole size of the character set; adding symbols to the set only widens it a little.

Worked example: 12 lowercase letters give 26 to the power 12, about 95 quadrillion (9.5 × 10^16) combinations, or 12 × 4.70 = 56.4 bits. Eight characters drawn from all 95 printable keyboard characters give 8 × 6.57 = 52.6 bits. Four more plain letters beat a short "complex" password.

The times below assume an attacker with a leaked, weakly protected password file who can test 100 billion guesses a second. That is an assumption for illustration: real speed depends on the hashing method and hardware, and a site that uses a deliberately slow hash such as bcrypt cuts it enormously. The times are for trying every combination; on average a password falls in half that.

The table only applies to random passwords. "Rahul@1995" has 10 characters from a 95-character set, which a naive formula rates at about 66 bits, but an attacker never searches all of those. Even a generous pattern list (10,000 first names, with or without a capital, 10 common symbols and 100 years) is only 20 million guesses: a fraction of a second at the speed above. Developers storing passwords should use a slow hash; our comparison of MD5, SHA-256 and bcrypt explains why, and the bcrypt hash generator makes test hashes.

Passphrases: strong passwords you can remember

For the few passwords you type from memory, string together randomly chosen words, for example tamarind orbit staple quartz velvet. The words must be picked at random, by dice or a generator, not by you: song lyrics, quotes and film dialogue are all in cracking wordlists. With a 7,776-word list (such as the EFF's dice wordlist), each word adds about 12.9 bits.

The table shows why four words, the classic advice, falls short against fast offline cracking. Use at least five words for anything important and six for your password manager's master password. Add capitals or separators if a site insists; the strength comes from the number of random words. Six words also clears NIST's 15-character minimum with room to spare.

What the site's password tools do

Password generator

The password generator creates one password per click, always 16 characters long. Each character is picked from 87: the 26 capital letters, 26 small letters, 10 digits and 25 symbols (!@#$%^&*()-_=+[]{};:,.<>?), using your browser's cryptographic random number generator. If a password comes out without at least one capital, one small letter, one digit and one symbol, the tool throws it away and draws again, so every password passes sites with composition rules. That costs a fraction of a bit, leaving about 102.8 bits. The password is created in your browser and is not sent anywhere.

There is no setting for length or for which symbols to use. If a site caps passwords below 16 characters, delete characters from the end: the rest are still random, but check that all four character types survive if the site requires them. If a site rejects a particular symbol, generate a new password.

Password strength checker

The password strength checker looks at length and which kinds of characters you used, calculates entropy as if the password were random, and estimates crack time at 10 billion guesses a second. It flags only a short list of very common passwords such as password, 123456 and qwerty. It cannot see patterns: it rates "Rahul@1995" as "Good", with 66 bits and "95 years". Use it to compare random passwords of different lengths, never to approve one you made up.

PIN generator

The PIN generator gives one random 6-digit PIN per click, also from the cryptographic generator, with no length option. A random PIN beats 1234, 0000 or your birth year, but six digits are still only a million combinations, so a PIN depends on the bank or phone locking you out after a few wrong tries.

Password managers, two-factor authentication and passkeys

Password manager. It remembers a different random password for every site and fills it in for you, and many flag reused or leaked passwords. Google Password Manager (in Chrome and Android) and Apple's Passwords app are built in; dedicated managers such as Bitwarden work across all your devices. Protect the manager with a six-word passphrase and two-factor authentication.

Two-factor authentication (2FA). A second step, usually a code, means a stolen password alone isn't enough. An authenticator app is safer than SMS codes, which can be intercepted through SIM-swap fraud. Never read an OTP out to anyone who calls you, whoever they claim to be.

Passkeys. A passkey replaces the password with a cryptographic key stored on your phone or computer, which you release with your fingerprint, face or screen lock. It only works on the genuine website, so it can't be phished, and there is nothing to leak or reuse. Google, Apple and Microsoft accounts support passkeys, and more sites add them every year; switch them on wherever you see the option.

A 15-minute password clean-up

1. Start with your main email account, because every other account's "forgot password" link goes there. Give it a new random password or a six-word passphrase, and turn on 2FA or a passkey.
2. Do the same for net banking and your password manager.
3. Check your email address on Have I Been Pwned to see which breaches it appears in, and change those passwords first.
4. Replace every reused password, one site at a time, with a generated one saved in your manager.
5. Delete accounts you no longer use.

Frequently asked questions

How long should a password be in 2026?

At least 15 characters if it is the only thing protecting the account, which is NIST's minimum. In practice, use 16 or more random characters from a generator, or five to six random words for passwords you must remember.

Should I change my passwords every 90 days?

No. NIST's guidance says systems must not force periodic changes, because people respond with Password1, Password2 and so on. Change a password immediately if the site reports a breach or you suspect someone else has it.

Is a passphrase better than a random password?

For passwords you have to remember, yes: six random words give about 77.5 bits and are far easier to type than 12 random symbols with similar strength. For passwords stored in a manager, a random 16-character string is shorter for the same strength.

Is it safe to use an online password generator?

Only one that creates the password on your device. Ours runs in your browser with its cryptographic random number generator and sends nothing to a server; it keeps working even if you go offline after the page has loaded.

Do symbols make a password stronger?

A little. Moving from 26 lowercase letters to all 95 keyboard characters adds about 1.9 bits per character, while each extra lowercase letter adds 4.7 bits. Length is the cheaper way to get strength.

Sources: NIST SP 800-63B-4, Digital Identity Guidelines: Authentication and Authenticator Management (final, July 2025); EFF large wordlist for dice-generated passphrases (7,776 words).