Password Strength Checker — Test & Generate Secure Passwords Free

Password strength is measured in bits of entropy — a mathematical way of expressing how unpredictable a password is. The higher the entropy, the more guesses an attacker would need to crack it through brute force. A password with 40 bits of entropy has about 1 trillion possible values; one with 80 bits has over a quintillion. Our tool calculates entropy based on the length of your password and the size of the character set you use (lowercase, uppercase, digits, symbols).

Knowing your password's entropy is more useful than a simple "weak/strong" label because it gives you a concrete number to work with. Security guidelines from NIST and major cybersecurity frameworks recommend at least 64 bits of entropy for standard accounts and 80 or more bits for high-value accounts like email, banking, or admin credentials.

This checker is useful for anyone who creates passwords — which is everyone. It is especially helpful for developers and IT professionals setting password policies, individuals who want to audit existing passwords before using a password manager, students learning about cybersecurity fundamentals, and teams writing internal security documentation or training materials.

Because the tool runs entirely in your browser and never transmits anything to a server, it is safe to test your actual passwords. The analysis happens in JavaScript on your device, so disconnecting from the internet does not affect functionality.

The tool counts the character set size your password draws from. A lowercase-only password uses a charset of 26; adding uppercase brings it to 52; adding digits gives 62; adding common symbols expands it to around 94. Entropy is then calculated as length × log₂(charset size). A 12-character password using all four character types gives roughly 79 bits of entropy — considered strong. The crack time estimate converts entropy into approximate guessing time assuming a modern GPU capable of billions of attempts per second.

• Length beats complexity — adding one more character is more effective than adding a symbol.
• Avoid dictionary words — even with substitutions like @ for a, these patterns are well known to attackers.
• Use passphrases — four random words like "lamp-cloud-river-fork" are both memorable and highly resistant to brute force.
• Use a password manager — tools like Bitwarden or 1Password generate and store high-entropy passwords so you never have to remember them.
• Never reuse passwords — a strong unique password per site limits damage if one site is breached.