Password Entropy Calculator
Calculate password entropy and strength rating.
About this tool
Password entropy measures how many bits of randomness a password has, based on its length and how large a character set it's drawn from \u2014 a useful, objective measure of resistance to brute-force guessing, independent of whether the password happens to spell a real word.
Key Features
- Entropy in bits from length and character set
- Qualitative strength rating
- No password is ever sent anywhere \u2014 calculated entirely from length and checkbox settings, not the actual password text
How to Use
- Enter the password length.
- Check which character types it includes.
- Click Calculate Entropy.
Benefits
- Understand what actually makes a password strong (length matters most)
- Compare entropy across different password policies
- See why 'P@ssw0rd!' style substitutions add little real entropy over the base word
Frequently Asked Questions
Entropy from character set and length can be calculated without ever seeing the real password \u2014 typing your actual password into any web tool is an unnecessary risk this calculator deliberately avoids.
It measures resistance to random brute-force guessing, but not resistance to dictionary attacks or leaked-password lists \u2014 a long password built from a common phrase can have high theoretical entropy from this formula while still being easier to guess than pure randomness suggests. Length plus true randomness (like a password manager generates) is what this measure best predicts.