Password Length Recommendation Calculator
Find the minimum password length needed to reach a target entropy for any character set.
How it works
Bits per character = log₂(charset size) · Length = ⌈target bits ÷ bits per character⌉
Each randomly chosen character contributes log₂(charset size) bits of entropy: about 3.3 bits for a digit, 4.7 for a lowercase letter and 6.55 for a full ASCII character. Dividing your target entropy by the per-character value and rounding up gives the shortest password that reaches the goal. This only holds when every character is chosen at random — patterns, dictionary words and keyboard walks collapse the real entropy far below the theoretical figure.
Worked example
For 80 bits from the full 94-character ASCII set, each character is worth log₂(94) ≈ 6.55 bits, so you need ⌈80 ÷ 6.55⌉ = 13 characters, which actually delivers about 85 bits. A digits-only PIN would need ⌈80 ÷ 3.32⌉ = 25 digits for the same strength.
Frequently asked questions
How long should my password be?
For most accounts a 12–16 character random password from a mixed set (upper, lower, digits, symbols) exceeds 80 bits and is very safe. For master passwords or encryption keys, aim for 100+ bits, which means roughly 16+ mixed characters.
Why does a longer password beat a more complex short one?
Length adds entropy multiplicatively — each extra character multiplies the search space by the charset size. Adding one character to a 94-symbol password adds about 6.5 bits, often more than switching a short password to a bigger character set.
Does this assume the characters are random?
Yes. The math is an upper bound that only applies to characters chosen uniformly at random, such as those from a password manager. Human-chosen passwords have far less real entropy than their length implies.
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This calculator is for educational purposes. Double-check important results before acting on them.