Password Entropy Calculator
Calculate password entropy to measure password strength. Entropy measures the randomness and unpredictability of a password, indicating how difficult it is to guess or crack.
Password is not stored or transmitted
How to Use This Calculator
- Enter your password in the input field (password is not stored or transmitted).
- The calculator analyzes the character set (lowercase, uppercase, digits, special characters).
- It calculates entropy in bits and categorizes password strength.
- Use this to evaluate password strength and understand how different character sets affect security.
Password Entropy Formula
Password entropy is calculated from length and character set size:
Example: 12-character password with lowercase, uppercase, digits, and special (94 possible characters): Entropy = 12 × log₂(94) = 12 × 6.55 = 78.6 bits. A 16-character password with the same set: Entropy = 16 × 6.55 = 104.8 bits.
Full Description
Password entropy is a measure of password strength that quantifies how difficult a password is to guess or crack through brute force attacks. It's expressed in bits, where each bit doubles the number of possible passwords. Higher entropy means stronger passwords that require more attempts to crack.
Entropy depends on two factors: password length and character set size. Longer passwords and larger character sets (including lowercase, uppercase, digits, and special characters) increase entropy. However, entropy is a theoretical measure—real-world password strength also depends on avoiding common patterns, dictionary words, and personal information. A password with high entropy but predictable patterns may still be vulnerable to dictionary attacks.
This calculator helps you evaluate password strength by calculating entropy. Enter your password, and it analyzes the character set, calculates entropy in bits, and categorizes strength. Use it to understand password security, evaluate password policies, or learn how different factors affect password strength. Remember that entropy is one factor—also use unique passwords, enable 2FA, and follow security best practices.
Frequently Asked Questions
What is password entropy?
Password entropy measures the randomness and unpredictability of a password, expressed in bits. Higher entropy means a stronger password that's harder to guess or crack. Entropy = Length × log₂(Character set size).
What is a good password entropy?
Very Weak: <40 bits. Weak: 40-60 bits. Moderate: 60-80 bits. Strong: 80-128 bits. Very Strong: 128+ bits. For most purposes, aim for at least 60-80 bits. Critical systems may require 128+ bits.
How does character set affect entropy?
Larger character sets increase entropy. Lowercase only (26 chars) = lower entropy. Adding uppercase (52 chars) doubles possibilities. Adding digits (62 chars) increases more. Adding special characters (94 chars) maximizes entropy per character.
Is entropy the only factor in password strength?
No. Entropy measures theoretical strength, but real-world strength also depends on: password patterns (avoid dictionary words, common patterns), uniqueness (don't reuse passwords), and protection against attacks (use 2FA, secure storage).