Measuring Password Strength

Strength is not a feeling — it is a number. This password entropy calculator computes the bits of unpredictability in any password and converts them into the time a determined attacker would need to brute-force it.

The Math

Entropy = length × log₂(charset size). Each of the 26 lowercase letters contributes 4.7 bits; adding uppercase, digits, and symbols grows the charset logarithmically. The crack-time estimate divides the guess space by a realistic 10-billion-guesses-per-second attack.

The Honest Caveat

Entropy math assumes random selection. Real attackers try dictionary words, leaked passwords, and patterns first — "Password1!" has high nominal entropy and near-zero real strength. Use a password manager's random generator; this calculator is the yardstick for what it produces.