What Makes a Strong Password? Length, Entropy & Pitfalls
What is a strong password? This guide explains password strength in terms of entropy (randomness from length and character set) and how to avoid common weaknesses.
A password’s "strength" is essentially how hard it is to guess, usually measured in "entropy" (bits). The more entropy, the longer brute-force attacks take.
Entropy is driven by two factors: length, and the variety of characters (the size of the character set). Roughly: entropy ≈ length × log₂(character set size). For example, a 12-character password with upper/lowercase letters + digits + symbols has about 12 × log₂(94) ≈ 78 bits of entropy — quite secure.
Common weaknesses include dictionary words, names or birthdays, reusing one password everywhere, and short length. The cheapest way to boost strength is usually to "get longer" rather than chase fancy symbols.