Password Strength Checker
Check how strong your password is against common attacks.
Password Strength Checker
What Is the Password Strength Checker?
A password strength calculator estimates how resistant a password is to guessing attacks by measuring length and character variety. The mathematics comes down to entropy in bits: each additional character multiplies the search space, and expanding the character set from lowercase only to full mixed case, digits, and symbols raises it further. Modern guidance from standards bodies has shifted emphasis toward length over exotic symbols, since memorable long passphrases outperform short complex strings both mathematically and behaviorally. This tool scores your password honestly, shows the estimated bits of entropy, and explains which changes buy the most security for the effort.
Key Statistics
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56 bits
Entropy of twelve random lowercase letters
Source: Calculated as 12 times log2 of 26
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52 bits
Entropy of eight characters drawn from the full printable keyboard set
Source: Calculated as 8 times log2 of 94
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Length first
Current NIST digital identity guidance favors longer passwords over forced complexity rules
Source: NIST SP 800-63B
The Formula
Score based on length, use of uppercase/lowercase/numbers/symbols, common patterns, and dictionary words.
Worked Examples
The password P@ssw0rd123 scores low because it relies on simple character substitutions of the common word password with predictable patterns. A strong 16 character password like J8k hash mP2 dollar vL9xQ bang rF uses mixed case, numbers, and symbols in random order for excellent security against brute force and dictionary attacks.
Comparing two passwords
- An eight character random mix from all key types yields about 52 bits
- A twelve character random lowercase string yields about 56 bits
- The longer simpler string wins despite using fewer symbol types
Adding length beats adding symbol soup.
Real World Use Cases
New account setup
Test candidate passwords before trusting anything important to them.
Passphrase design
Check entropy of word based passphrases built from random word picks.
Security training
Demonstrate concretely why length and randomness beat clever substitution.
Expert Tips
- ✓ Use a password manager to generate and store truly random strings so memory limits stop constraining strength.
- ✓ Never reuse passwords across sites; breach reuse is the most common compromise path in practice.
- ✓ Dictionary words arranged predictably add far less entropy than their length suggests.
- ✓ Enable multi factor authentication everywhere; it rescues even mediocre passwords from most attacks.
Frequently Asked Questions
What makes a password strong? ▼
Length is the biggest factor, so aim for at least 12 characters, then mix upper and lower case letters, numbers, and symbols, and avoid common words, sequences, and personal details. A random passphrase of several words is both strong and memorable.
How strong is my password? ▼
Strength is measured in entropy, the number of bits of randomness. Under about 40 bits is weak, 60 to 80 bits is solid for most accounts, and 100 bits or more is effectively uncrackable by brute force.
Why does length matter more than special characters? ▼
Each extra character multiplies the number of possible combinations, so adding length grows the search space far more than swapping in symbols. A long passphrase beats a short, symbol heavy password every time.
What is password entropy? ▼
Entropy measures how unpredictable a password is, in bits. It is the log base 2 of the number of possible guesses, and each extra bit doubles the work an attacker must do to guess it.
Is my password sent anywhere? ▼
No. This checker runs entirely in your browser, so the password you test is never transmitted, logged, or stored. You can disconnect from the internet and it still works.
Should I reuse passwords across sites? ▼
No. If one site is breached, attackers try the same password everywhere, a practice called credential stuffing. Use a unique password per account and a password manager, and turn on two factor authentication.
How long should a password be? ▼
Fourteen or more random characters, or four or more randomly chosen unrelated words, provides strong practical protection today.
Does adding symbols always help? ▼
Symbols raise entropy per character, but two extra length usually beats two extra symbol types while staying easier to remember.
Common Mistakes to Avoid
- ⚠ Using a password that scores highly but contains personal information like your name or birth year. An algorithm cannot know those details, so a password the checker calls strong may still be guessable by someone targeting you.
- ⚠ Treating a high score as permission to reuse the same password across multiple sites. Strength checks measure complexity, not uniqueness. A breached password is compromised everywhere regardless of its score.
- ⚠ Ignoring the specific suggestions the checker provides and only looking at the strength label. A medium score with clear fixable issues like short length or missing symbols is far easier to improve than chasing an arbitrary high score with random character spam.
- ⚠ Substituting lookalike characters in dictionary words. Attackers try those patterns automatically, so P4ssw0rd style tweaks add nearly nothing.
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Last updated: · by CalculatorPro Tools