Password Strength Calculator

Password entropy is the gold standard for measuring password strength. Our password entropy calculator shows exactly how many bits of randomness your password contains.

More entropy bits means exponentially more combinations an attacker must try. Aim for 80+ bits for important accounts.

How long would it take to crack your password? Our brute force time calculator estimates crack time based on modern GPU clusters (10 billion guesses/second).

See the dramatic difference between a 6-character password (minutes) and a 16-character password (centuries).

The best passwords combine length with complexity. Use 12+ characters mixing uppercase, lowercase, numbers, and symbols. Or use a passphrase of 4+ random words.

Avoid personal info, common words, and predictable patterns. Our password strength tester shows exactly what makes your password strong or weak.

Password entropy is a measurement of unpredictability, expressed in bits, that estimates how hard a password is to guess. It is calculated as E = L × log2(R), where L is the password length and R is the size of the character pool (26 lowercase, 26 uppercase, 10 digits, and roughly 33 common symbols).

Each extra bit of entropy doubles the number of guesses an attacker must make. This information-theoretic model traces back to Claude Shannon's foundational work on information theory, and NIST SP 800-63B discusses password strength in terms of guessing resistance rather than rigid composition rules.

Higher entropy consistently means a more resilient password.

A brute-force attack cracks passwords by systematically trying every possible character combination until one matches. Attackers rarely start blindly, though: they first run dictionary and rule-based attacks with tools like Hashcat or John the Ripper, testing leaked password lists and common substitutions before falling back to exhaustive search.

Modern GPU clusters can compute billions of hash guesses per second, which is why short passwords fall quickly. According to OWASP guidance, defenders should slow attackers by hashing stored passwords with memory-hard algorithms such as bcrypt, scrypt, or Argon2 rather than fast hashes like MD5 or SHA-1.

Entropy determines how many guesses brute force ultimately requires.

Password length increases strength faster than adding special characters because entropy scales linearly with length but only logarithmically with the character pool. Adding one more character to a lowercase password roughly multiplies the search space, whereas swapping a letter for a symbol adds only a fraction of a bit.

NIST SP 800-63B reflects this by removing mandatory complexity rules and instead encouraging longer passwords and passphrases of up to 64 characters or more. A 20-character all-lowercase phrase can outmatch an 8-character password stuffed with symbols.

For memorable strength, prioritize length first, then variety second.

Passphrases are often more secure and more usable than short complex passwords because their length delivers high entropy while remaining memorable. A passphrase of four or more truly random words drawn from a large wordlist, such as the EFF Diceware lists, yields strong entropy without requiring you to memorize awkward symbol strings.

The key is randomness: a quoted movie line or a common phrase offers little protection because attackers include such phrases in their dictionaries. NIST SP 800-63B explicitly supports long memorized secrets and allows spaces.

Choose independent, randomly selected words rather than a grammatically meaningful sentence.

Password hashing protects stored credentials by converting a password into a fixed-length, irreversible value, so a database breach does not directly expose plaintext passwords. A salt, a unique random value added to each password before hashing, prevents attackers from using precomputed rainbow tables and ensures identical passwords produce different hashes.

OWASP recommends slow, memory-hard functions like Argon2id, bcrypt, or scrypt, tuned so each hash is expensive to compute. Fast hashes such as MD5 and SHA-1 are unsuitable for passwords because they let attackers test billions of guesses per second.

This calculator estimates guessing difficulty, not the strength of any server-side hashing.

No, you should never reuse passwords across accounts, because a single breach then compromises every site sharing that credential. Attackers exploit this with credential stuffing, replaying username and password pairs leaked from one service against many others using automated tools.

OWASP identifies credential stuffing as a major cause of account takeover, and unique passwords are the primary defense. A password manager solves the memory problem by generating and storing a distinct high-entropy password for every login.

Pairing unique passwords with multi-factor authentication, as recommended by NIST and OWASP, dramatically reduces the impact of any single data breach.

Your results combine three complementary signals:

• an entropy value in bits
• a qualitative strength rating
• an estimated crack time

Entropy is the objective core measurement, while the rating (weak through very strong) and crack-time estimate translate those bits into intuitive terms based on an assumed guessing rate. Because attacker hardware varies enormously, crack-time figures are order-of-magnitude guides, not guarantees, and align with the guessing-resistance philosophy described in NIST SP 800-63B.

Use the entropy number to compare candidate passwords, treat anything under 60 bits as risky for important accounts, and aim for 80 or more bits where security matters most.

The most common password mistakes are predictable choices that attackers already anticipate:

• Avoid dictionary words, sequential keys like qwerty or 123456, and personal details such as names, birthdays, or pet names that appear in breach dumps and social media.
• Simple character substitutions (@ for a, 3 for e) add negligible entropy because cracking tools apply these rules automatically.
• Do not merely append a number or exclamation mark to a weak base word, and never reuse an old password.

OWASP recommends checking new passwords against known-breached lists, and NIST advises screening against compromised credential databases before accepting them.