Password Entropy Calculator
Length (characters):0
Character space size:0
Entropy:0 bit
Rating:—
Estimated time to crack:—
Calculation assumes random characters (length × log₂ character space). Real words/patterns are weaker. Crack time at 10 billion guesses/sec. All local – no password leaves the browser.
How password entropy is calculated
Entropy measures the unpredictability of a password in bits. The more bits, the more attempts an attacker needs on average. The formula: length × logarithm base 2 of the character-space size.
- Character space: lowercase (26) + uppercase (26) + digits (10) + symbols (~33). The more classes, the larger the space.
- Rule of thumb: Below 28 bits very weak, from 60 bits strong, from 128 bits very strong.
- Limitation: The calculation assumes true randomness. "Password123!" has many bits on paper but is easily cracked by dictionary attacks.
For strong, random passwords, use our password generator or XKCD passphrase generator.