Password Entropy Calculator

Calculate password entropy and bit strength.

Security

About Password Entropy

Password entropy is a measure of randomness expressed in bits. Each bit doubles the number of possible combinations an attacker must try. A password with 40 bits of entropy has 240 (about one trillion) possible values, while 80 bits yields 280 — an astronomically large number. By estimating the character pool (lowercase = 26, add uppercase = 52, add digits = 62, add symbols = 95+) and multiplying by the password length, we derive the total entropy. This metric helps you compare the relative strength of different passwords and decide whether yours meets the security requirements of your accounts.

How to Use Password Entropy Calculator

  1. Type or paste your password in the Password field. Toggle Show password if you want to see the characters.
  2. The entropy score (in bits) updates in real time as you type.
  3. Aim for at least 50–60 bits for everyday accounts and 70–80+ bits for high-security applications like master passwords.
  4. If the score is low, increase the length or add more character types (uppercase, digits, symbols).

Key Features

  • Real-time entropy calculation as you type — no button click required
  • Detects character classes automatically (lowercase, uppercase, digits, symbols)
  • Displays result in bits for easy comparison with security guidelines
  • Show/hide toggle to keep your password private on shared screens
  • 100% client-side — your password never leaves your browser

When to Use This Tool

  • Evaluating the strength of a new password before using it
  • Comparing different password strategies (random characters vs. passphrases)
  • Meeting specific entropy requirements set by your organization's security policy
  • Teaching or learning about information theory and password security
  • Auditing existing passwords to identify weak ones that need replacement

Technical Details

The calculator estimates the character set size from the types of characters present: 26 for lowercase, 26 for uppercase, 10 for digits, and 33+ for symbols. Entropy is computed as length × log₂(charset_size). This is an upper-bound estimate assuming each character is chosen randomly from the full set — passwords with patterns, dictionary words, or repeated characters have lower effective entropy. For a complementary qualitative assessment, try the Password Strength Checker.

Conclusion

Understanding password entropy helps you make informed decisions about credential security. This free, browser-based calculator gives you an instant numerical score so you can objectively evaluate and improve your passwords — all without any data leaving your device.

Frequently Asked Questions

What is password entropy?
Entropy measures unpredictability in bits. More bits mean more possible combinations and a stronger password. Each additional bit doubles the number of guesses an attacker would need to try.
How is it calculated?
The tool estimates the character set size from what you type (e.g. lowercase only = 26, add uppercase = 52, add digits = 62, add symbols = 95+). Entropy equals length × log₂(charset size).
What is a good entropy score?
For general accounts, aim for at least 50–60 bits. For sensitive accounts and master passwords, 70–80 bits or higher is recommended. Above 100 bits is considered extremely strong.
Is my password sent anywhere?
No. The calculation is done entirely in your browser using JavaScript. Your password never leaves your device and is never stored.