Password Entropy Calculator
Password Entropy FAQ
What is password entropy?
Password entropy measures the unpredictability of a password in bits. The higher the entropy, the stronger the password.
How is entropy calculated?
Entropy is based on the size of the character set and the password length. Formula: Entropy = length × log2(characterSetSize).
What is a good entropy value?
40–60 bits is considered moderate, 60–80 bits strong, and 80+ bits very strong.
Understanding Password Entropy
Understanding Password Entropy
Password entropy is a mathematical measurement that reflects the strength and unpredictability of a password. It combines two important factors:
- Password length — the total number of characters.
- Character variety — the size of the alphabet used (e.g., lowercase only vs. lowercase + uppercase + digits + symbols).
The higher the entropy, the more difficult it becomes for an attacker to guess or brute-force your password. Entropy is usually measured in bits, where each additional bit effectively doubles the search space an attacker must attempt.
Why Entropy Matters
Short or predictable passwords are quickly broken by automated tools. By contrast, longer passwords with diverse character sets generate exponentially higher entropy, making them resilient even against powerful GPUs or distributed cracking clusters.
Examples of Password Entropy
| Password Example | Character Set | Length | Entropy | Estimated Crack Time |
|---|---|---|---|---|
password | Lowercase only (26) | 8 | ≈ 37 bits | Seconds |
P@ssw0rd! | Mixed (94) | 9 | ≈ 59 bits | Days |
kD9!xR7Q&Zm2 | Mixed (94) | 12 | ≈ 78 bits | Thousands of years |
correct horse battery staple | Words + spaces | 25+ | 100+ bits | Practically uncrackable |
How to Increase Password Entropy
- Make it longer — each extra character dramatically increases entropy.
- Mix character types — combine lowercase, uppercase, digits, and special symbols.
- Avoid dictionary words — common words and phrases drastically lower entropy.
- Use passphrases — combining random words creates high-entropy passwords that are still memorable.
About This Tool
This password entropy calculator lets you instantly measure the strength of your password. By analyzing length and character set, it provides a clear entropy score (in bits) and an estimated crack time. All calculations happen entirely in your browser, ensuring that your input never leaves your device.
Whether you are improving personal account security, designing corporate password policies, or simply testing password strength, this tool gives you actionable insight into how entropy works and why it is the foundation of password security in 2025.