Password Entropy Calculator

The password entropy calculator measures how hard a password is to guess by working out its entropy in bits, the standard way security professionals describe strength. Entropy depends on two things, how long the password is and how large the pool of possible characters is, so a long password drawn from a mix of cases, digits and symbols scores far higher than a short word. The tool inspects your password, counts which character types it uses, lowercase, uppercase, digits and symbols, and adds up the size of that combined pool. It then multiplies the length by the base two logarithm of the pool size to give the entropy in bits, where each extra bit doubles the number of guesses an attacker would need. Alongside the bit count you get a plain strength rating and a rough estimate of how long a fast offline attack at ten billion guesses a second would take on average, which turns an abstract number into something you can feel. Anyone choosing a password for email, banking or a work login can use it to sanity check a choice before committing to it. A few habits make a real difference. Favour length over complexity, because adding characters raises entropy faster than swapping a letter for a symbol. Use a passphrase of several unrelated words, or let a password manager generate a long random string. Never reuse a strong password across sites, since one breach then exposes them all. This tool runs entirely in your browser and the password you type is never sent anywhere, but you should still avoid pasting a real password you currently use into any website.

Entropy = length x log2(character pool size). Crack time assumes ten billion guesses a second, on average. Rough guide only, not a security guarantee.