See how long it would take a computer to crack your password.
Password cracking speed depends on the hashing algorithm used and the attacker's hardware. This calculator assumes a fast offline attack at 10 billion guesses per second, which is realistic for a modern GPU cluster attacking MD5 hashes. Against properly salted bcrypt hashes, times would be millions of times longer.
Length is the single most important factor. Each additional character multiplies the number of possible combinations exponentially. A 12-character password using uppercase, lowercase, numbers, and symbols has about 475 trillion times more combinations than an 8-character password using only lowercase letters. Use a passphrase of 4+ random words, or a password manager that generates random strings of 16+ characters.