What Makes a Password Strong? Standards, Guidelines, and Best Practices
"Strong password" is a phrase thrown around constantly, but what does it actually mean? This article breaks down the technical definition of password strength, references the standards that security professionals follow, and explains how this generator produces passwords that meet those standards by default.
Defining Password Strength
Password strength is a measure of how resistant a password is to guessing or brute-force attacks. It is quantified in bits of entropy — a concept from information theory that represents the amount of unpredictability in a value. Each bit of entropy doubles the number of guesses an attacker needs. A password with 40 bits of entropy requires up to 2^40 (about one trillion) guesses, while 60 bits requires up to 2^60 (about 1.15 × 10^18).
The National Institute of Standards and Technology (NIST) publishes password guidelines in Special Publication 800-63B. The current revision shifted focus away from forced complexity rules (like requiring a mix of character types) toward length and uniqueness. NIST now recommends that organizations allow passwords of at least 8 characters, encourage longer passwords, and check new passwords against known breached password lists.
However, NIST guidelines are a floor, not a ceiling. They are designed for organizations managing thousands of users with varying technical literacy. For individual users who want strong security, 16+ characters with a full character set is a much better target than the 8-character minimum. You can test any password against these standards using our password strength checker.
Weak vs Strong Passwords: Side by Side
Consider the password P@ssw0rd1!. It is 10 characters long and includes uppercase, lowercase, numbers, and a symbol. Many websites would rate it as "strong" based on their simple complexity meters. But it is actually extremely weak — it is a dictionary word ("password") with predictable substitutions (a to @, o to 0) and an incrementing number. Every password cracking tool tests this pattern within the first few seconds.
Now consider k9$mP2#nQ8vR — 12 characters, same character types, but completely random. There is no dictionary word, no pattern, no personal information. An attacker would need to try an average of 94^12 / 2 (about 2.3 × 10^23) guesses to crack it. At a billion guesses per second, that would take roughly 7 million years.
The difference is not in the character types used — both passwords have the same mix. The difference is in predictability. The first follows a human pattern; the second is cryptographically random. This is why random generation matters more than meeting complexity requirements.
How This Strong Password Generator Works
This generator forces all four character types on by default — uppercase, lowercase, numbers, and symbols. This is different from the main generator on the home page, which lets you toggle individual types off. The reason for forcing is that many websites require all four types, and a password missing one type can be rejected at registration.
Beyond just including each character type somewhere in the password, the generator ensures that each type is represented. A purely random 12-character draw from 94 characters has a small but real chance of missing an entire category — for example, by chance containing no symbols. This generator guarantees inclusion by design, so every output meets the "strong" bar.
The randomness comes from the Web Crypto API, which provides a cryptographically secure random number generator. Each character position is filled by an independent random draw, making the output unpredictable to any attacker — even one who knows the exact algorithm being used.
Recommended Password Length by Use Case
- Low-value accounts (forums, throwaway registrations): 8-10 characters may suffice, though 12 is always better
- Social media and shopping accounts: 12-16 characters with full character set
- Email and banking accounts: 16-20 characters — these are the keys to your digital identity
- Password manager vault master password: 20+ characters, or use a 6-word passphrase from our passphrase generator
- Cryptocurrency wallets and root administrator accounts: 24+ characters or a 7+ word passphrase
The quick-select buttons on this page default to 12, 15, 16, and 20 characters. For most users, 16 is the sweet spot — long enough to resist offline cracking for decades, short enough to type or paste comfortably.
Character Types Explained
The full character set used by this generator includes 94 printable ASCII characters: 26 uppercase letters (A-Z), 26 lowercase letters (a-z), 10 digits (0-9), and 32 symbols. Each character type adds to the total character set size, which directly increases the entropy per character.
- Lowercase only (26 chars): 4.7 bits per character
- Lowercase + uppercase (52 chars): 5.7 bits per character
- Letters + numbers (62 chars): 5.95 bits per character
- Full set including symbols (94 chars): 6.55 bits per character
The jump from 62 to 94 characters adds less than one bit per character, which is why some security researchers argue that symbols matter less than length. However, many websites require symbols, and including them does add real difficulty for attackers who narrow their search to alphanumeric-only character sets.
The Mathematics of Password Entropy
Entropy is calculated as log2(charsetSize^length), which simplifies to length × log2(charsetSize). For the full 94-character set, each character contributes 6.55 bits. A 16-character password therefore has about 105 bits of entropy — more than enough to resist any feasible brute-force attack.
To put this in perspective: all the computing power on Earth, running for the age of the universe, could not check 2^128 combinations. A 16-character random password with 105 bits of entropy is well within that bound. Even if computing power continues to double every two years, a 16-character random password will remain uncrackable for the foreseeable future.
Why Strong Passwords Still Matter With 2FA
Two-factor authentication (2FA) adds a second layer of security, but it does not make weak passwords safe. 2FA can be bypassed through phishing, SIM swapping, or social engineering. If an attacker obtains your password through a phishing page, the 2FA code may also be captured in real time. Defense in depth means that each layer should be strong on its own — a strong password plus 2FA is far better than a weak password plus 2FA.
Additionally, some services use password-based encryption to protect your data at rest. If the service is breached and the password database is leaked, a strong password means the encrypted data remains protected even if the attacker has the hash. A weak password can be cracked from the hash offline, bypassing 2FA entirely.
Explore More Tools
Once you have a strong password, explore our other free tools. Generate memorable passwords for accounts you need to recall, secure your wireless network with our WiFi password generator, create credentials at scale with our bulk password generator, find a unique handle with our username generator, or build passwords from words you choose with our custom words password generator.