You have probably seen a password meter call something “strong” or “weak.” Behind that judgment is a real, measurable idea: entropy. It is the most honest way to talk about password strength, and once you get it, you will never be fooled by a “complex-looking” password again. Our GetMyPassword team explains what password entropy is and why it matters.
What password entropy is
Entropy is a measure of how unpredictable a password is, expressed in bits. Each extra bit doubles the number of possible combinations an attacker must try. A password with 40 bits of entropy has about a trillion possibilities; one with 80 bits has trillions of trillions. The higher the entropy, the longer a brute-force attack takes — from seconds to longer than the age of the universe.
What drives it: length and variety
Two things raise entropy: the size of the character pool (lowercase, uppercase, numbers, symbols) and, above all, the length. Length is the more powerful lever, because every added character multiplies the possibilities. This is why a long passphrase of random words beats a short string of symbols — even though the short one “looks” more complex.
Why “complex-looking” can fool you
- Predictable substitutions like P@ssw0rd add almost no real entropy — attackers expect them.
- Real randomness matters, not visual complexity; a pattern you invented is guessable.
- Length wins: a longer password beats a shorter “complex” one every time.
- Reuse erases it: high entropy means nothing if the password already leaked elsewhere.
Entropy measures true randomness, not how clever a password looks. The mind cannot generate it reliably — we fall into patterns. That is exactly the job a generator does better than any human.
How to get high entropy easily
You do not need to calculate bits — you need genuine randomness and length. The simplest path is to let our password generator create a long, truly random password for each account; it produces far more entropy than anything you would think up. Store them in a password manager, and your logins are strong in the way that actually counts, not just the way that looks impressive.
Frequently asked questions
What is password entropy in simple terms?
It is a measure of how unpredictable a password is, in bits. Each extra bit doubles the combinations an attacker must try, so higher entropy means a password is much harder to crack by brute force.
Does length or complexity matter more for entropy?
Length matters more. Each added character multiplies the possibilities, so a long passphrase usually has more entropy than a short symbol-heavy password. Both length and a varied character set help, but length is the stronger lever.
How much entropy should a password have?
More is better; many experts suggest aiming well above 60–80 bits for important accounts. The easiest way to reach high entropy is to use a long, truly random password from a generator rather than inventing one yourself.