Built and fact-checked by the DocNectar team — see our editorial standards
Key Features
Instant Calculation
Get accurate results in real time with our optimized algorithm.
Mobile Friendly
Fully responsive design. Works on all devices & screen sizes.
Privacy Focused
Your data stays on your device. We don't store any inputs.
100% Free
No hidden costs. This tool is completely free forever.
Password entropy is the quantitative, mathematical measure of how many guesses a brute force attack would need — a simple function of how long a password is and how large a character pool it draws from.
This calculator computes a password's theoretical entropy in bits, based purely on its length and detected character classes, with a full step-by-step solution.
How it works
Enter a password. The calculator detects which character classes appear (lowercase, uppercase, digits, symbols) to determine the pool size, then applies the entropy formula \(H = L \times \log_2(N)\), where L is the length and N is the pool size.
- Enter password.
- Click Calculate to see your results.
Examples
An 8-character all-lowercase password
An 8-character password using only lowercase letters (pool size 26) has an entropy of about 37.6 bits — "Reasonable" but not strong.
Who should use it
- Understanding the theoretical strength of a password candidate before adopting it.
- Comparing the entropy impact of adding length versus adding character variety.
Industry applications
- Information security and password policy education
- Software development and authentication system design
Advantages
- Simple, transparent, formula-based calculation.
- Reports the detected character pool size for full transparency.
Limitations
- A pure mathematical measure only — doesn't detect dictionary words or predictable patterns like the Password Strength Checker does.
Common mistakes to avoid
- Assuming high entropy alone guarantees a secure password — a long, high-entropy-looking password that's still a common dictionary phrase can still be guessed quickly by pattern-aware attacks.
- Using a very short password with many character classes, expecting it to score as strong — length matters more than pool size in the entropy formula.
Best practices
- Prioritize length over complexity — a longer password consistently produces more entropy than a shorter one with more symbol variety.
Tips
- To meaningfully increase entropy, add more characters rather than just swapping in more symbols — length has a larger multiplicative effect on entropy than pool size.