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Password Entropy Calculator

See how length and character variety translate into bits of entropy — no password needed, just the numbers.

STRENGTH—

—Entropy

—Crack Time

—Pool

—Combinations

Length16

1128

Uppercase

Lowercase

Numbers

Symbols

How it works

This calculator shows the theoretical entropy of a password built from a given length and character set — without needing you to type an actual password. Move the length slider and toggle character types to see how each choice changes the bits of entropy, the number of possible combinations, and the estimated time to crack at 10 billion guesses per second.

This is different from the strength checker: that tool analyses one specific password you type, including whether it looks like a dictionary word or a common pattern. This one answers a simpler question — "if I generate N random characters from this character set, how strong is that in theory?" — which is exactly what a good password generator relies on.

Related terms: Entropy · CSPRNG · Brute force · Key stretching

FAQ

What is password entropy?

It's a measure, in bits, of how unpredictable a password is — roughly the length multiplied by the base-2 logarithm of the character set size. Each extra bit doubles the effort needed to guess it by brute force.

Why does this tool give a different number than the strength checker?

The strength checker analyses a real password you typed and can penalise it for looking like a word or pattern. This calculator assumes every character is chosen uniformly at random from the selected set — the theoretical best case, which is what a good generator actually achieves.

How many bits of entropy is enough?

Around 60 bits is borderline for low-value accounts, 75–100 is strong for everyday use, and over 100 is appropriate for a master password or an encryption key.