How Long Should Your Password Actually Be? The Real Entropy Math
Every login form on the internet tells you to use a strong password. Almost none of them tell you what that actually means in numbers you could check for yourself. "Strong" ends up meaning whatever the site's password rules happen to enforce, eight characters, one number, one symbol, which is a rule of thumb dressed up as a standard. The real answer comes down to a specific, measurable quantity called entropy, and once you understand how it's calculated, the advice stops being vague.
Aim for at least 12 to 14 characters mixing uppercase, lowercase, digits and symbols, which typically clears 60 bits of entropy, the rough threshold considered genuinely strong against modern cracking hardware. Length matters more than complexity rules: each extra character multiplies the guessing difficulty far more than swapping a letter for a symbol does.
What is entropy, and why does it matter more than "complexity rules"?
The formal measure of randomness in a password is entropy, measured in bits. A coin flip has 1 bit of entropy, two equally likely outcomes. A six-sided die has approximately 2.58 bits. A four-character password drawn from a pool of 62 alphanumeric characters has log₂(62⁴), roughly 23.8 bits. An eight-character password from the same pool has 47.6 bits. This is not just a bigger number, each additional bit doubles the number of possible passwords, doubling the work an attacker must do. Entropy scales exponentially, which is why length consistently beats clever substitution tricks like swapping an "a" for an "@".
How many bits of entropy do you actually need?
A password of 60 or more bits is generally considered strong against realistic modern attacks. Below roughly 30 bits, any determined attacker with modest hardware will crack it quickly. To put concrete numbers on it: a twelve-character password mixing uppercase, lowercase, digits and symbols, drawn from a roughly 94-character set, works out to log₂(94¹²), which lands comfortably above 75 bits, well past the strong threshold. An eight-character password from the same set only reaches around 52 bits, noticeably weaker despite looking similarly complex at a glance.
What actually went wrong in the LinkedIn breach?
In 2012, LinkedIn suffered a breach in which 6.5 million password hashes were stolen and posted to a Russian forum. The hashes were SHA-1, fast and inadequate by modern standards, but the truly damning detail was that LinkedIn had not salted them properly. A salt is a random string added to a password before hashing, so that two users with the same password produce different hashes. LinkedIn had used sequential, predictable salts. Attackers who cracked one hash often found they had accidentally cracked thousands of others. The predictability in the salt, the appearance of randomness without the substance, multiplied the damage catastrophically, regardless of how strong any individual user's password was.
Is a passphrase of real words a shortcut to strong entropy?
It can work, but only if the words are genuinely randomly selected, not a phrase a person would naturally think up. Four words picked truly at random from a list of a few thousand common words can reach entropy comparable to a shorter fully random password, because the math is based on how many possible combinations exist, not on whether the result happens to be pronounceable. The catch is that human-generated "random" word choices are far less random than they feel. People gravitate toward the same handful of memorable words, which quietly collapses the effective entropy far below what the math promises on paper.
Does client-side generation actually matter for password security?
There's one more distinction worth knowing: client-side generation versus server-side generation. When a tool generates a password entirely in your browser, using the browser's own cryptographic random number generator, with no data sent to any server, the password never travels across the network during creation. It can't be logged, intercepted, or stored in a database you don't control before you've even used it. For something as sensitive as a password, where it's generated is nearly as important as how.
The password generator on this site works entirely client-side and includes a live entropy strength meter, so you can see in real time exactly how much randomness a given length and character set actually produces, rather than guessing based on a site's arbitrary complexity rules.
Frequently Asked Questions
How many characters should a strong password have?
For an important account, aim for at least 12 to 14 characters drawn from a full mix of uppercase, lowercase, digits and symbols. That combination typically clears 60 bits of entropy, which is the rough threshold security researchers consider genuinely strong against modern cracking hardware.
Does adding symbols actually make a password stronger, or just harder to type?
It does both, but the strength gain is real, not cosmetic. Moving from a 26-letter alphabet to a roughly 94-character set that includes symbols increases the number of guesses an attacker needs for every additional character, which compounds fast across a whole password.
Is a long passphrase of real words better than a short random password?
It can be, if it's genuinely long. A four-word passphrase drawn from a large word list can reach similar entropy to a shorter fully random password, but it needs to be four truly random words, not a memorable phrase a person would naturally think of, since the latter is far more guessable than the math suggests.
Why did the LinkedIn breach matter so much for password advice?
Because it showed encryption strength alone doesn't save you if the surrounding implementation is careless. LinkedIn's 2012 breach exposed password hashes that were improperly salted, meaning identical passwords produced identical hashes across different accounts, so cracking one password often cracked thousands of others at once.
What is entropy, in plain terms?
It's a measure of how many guesses an attacker would need, on average, to find your password by brute force, expressed in bits. Each additional bit doubles the number of possible passwords, so entropy grows exponentially, not linearly, as you add length or character variety.
Is it safe to reuse a strong password across multiple sites?
No, regardless of how strong the password itself is. If any one of those sites suffers a data breach, every other account using that same password becomes vulnerable too. A password manager makes using a different strong password per site practical without needing to memorise all of them.