How long should a password be?
For a randomly generated password: at least 16 characters for important accounts, and longer costs you nothing if a password manager fills it in.
Length beats complexity
Each extra character multiplies the number of possible passwords by the size of the character set. Adding symbols to a password helps, but adding length helps more: an 18-character password of lowercase letters alone is stronger than a 12-character password using every character type.
| Length | Lowercase only | Letters and numbers | Letters, numbers and symbols |
|---|---|---|---|
| 8 | 37 bits · Weak about 1 second | 47 bits · Weak about 18 minutes | 51 bits · Fair about 5 hours |
| 10 | 47 bits · Weak about 12 minutes | 59 bits · Fair about 49 days | 64 bits · Fair about 5 years |
| 12 | 56 bits · Fair about 6 days | 71 bits · Fair about 511 years | 77 bits · Strong about 39,133 years |
| 14 | 65 bits · Fair about 10 years | 83 bits · Strong about 2 million years | 90 bits · Strong about 310 million years |
| 16 | 75 bits · Strong about 6,909 years | 95 bits · Strong about 7.6 billion years | 103 bits · Very strong longer than the age of the universe |
| 20 | 94 bits · Strong about 3.2 billion years | 119 bits · Very strong longer than the age of the universe | 129 bits · Very strong longer than the age of the universe |
| 24 | 112 bits · Very strong longer than the age of the universe | 142 bits · Very strong longer than the age of the universe | 155 bits · Very strong longer than the age of the universe |
Weak under 50 bits · Fair 50–74 bits · Strong 75 bits or more, which is what to aim for.
Average time to crack a randomly generated password offline at 100 billion guesses per second: a well-funded attacker against a fast, unsalted hash. Human-chosen passwords fall far faster than this table suggests, because attackers try likely passwords first.
Recommendations
- Accounts in a password manager: 20 random characters. You never type them, so there's no reason to go shorter.
- Important accounts (email, banking, cloud storage): at least 16 random characters, plus two-factor authentication.
- Passwords you type or remember: a passphrase of six or more random words.
- Sites with a maximum length: use the longest allowed.
What "bits of entropy" means
Entropy measures how many possible passwords a method could have produced. A password with
n bits is one of 2n equally likely possibilities, so an attacker needs on
average 2n−1 guesses. It describes the method, not the string: Tr0ub4dor&3
looks complex, but it follows a pattern attackers know. That's why the figures here only apply
to randomly generated passwords.