Password Entropy Calculator

Password entropy measures the information content of a password in bits. It is calculated as the logarithm base 2 of the total number of possible passwords: E = L * log2(C), where L is the password length and C is the number of possible characters at each position. A password with 1 bit of entropy has 2 possible values. Each additional bit doubles the number of possibilities. At 40 bits of entropy, there are about 1 trillion possibilities. At 80 bits, there are about 10^24 possibilities. The character set size depends on what characters are used. Lowercase letters provide 26 options per character. Adding uppercase doubles it to 52. Adding digits brings it to 62. Including symbols (such as !@#$%^&*) increases it further. The full printable ASCII set provides 95 options per character position. Password length has a more significant impact on entropy than character set size because it appears as the exponent. Increasing a 10-character password to 12 characters with the same character set adds more entropy than keeping 10 characters and adding symbols. Modern password cracking can test billions of passwords per second using GPUs. A password with 40 bits of entropy can be cracked in seconds. Fifty bits takes hours, sixty bits takes months, and eighty bits is considered infeasible with current technology. This calculator assumes truly random passwords. Human-chosen passwords are far weaker because people use patterns, dictionary words, and predictable substitutions that attackers exploit.