Password Entropy Calculator
Bits of entropy from length and character set — with the formula shown, not hidden.
How it works
Entropy is a measure of unpredictability, in bits. For a password chosen uniformly at random it is
length × log2(pool), where the pool is how many different characters each position
could hold. Enabling a character class adds its size to the pool: lowercase and uppercase are 26 each,
digits 10, and the common symbol set about 33 — a full pool is roughly 95. Each bit doubles the number of
guesses an attacker must make, so 40 bits is a thousand times harder than 30. The calculator shows the
formula with your numbers filled in, the total keyspace as a power of two, and where the result lands on a
strength scale. Because it assumes true randomness, treat it as a ceiling — real, self-chosen
passwords fall short of it.
FAQ
How is password entropy calculated?
Entropy in bits = length × log2(pool size), where the pool is the number of distinct
characters the password could draw from: 26 for lowercase, 26 for uppercase, 10 for digits, and about 33
for symbols. A 16-character password from a 95-character pool is 16 × log2(95), roughly
105 bits.
Does this apply to a password I chose myself?
Only as an upper bound. The formula assumes every character is chosen uniformly at random. A human-picked password of the same length carries far less real entropy because words, names, and patterns are predictable — use the strength checker for a pattern-aware estimate of a specific password.
Is adding symbols better than adding length?
Length is the stronger lever. Adding one character multiplies the keyspace by the whole pool size, while switching pools only changes the per-character log. Going from 12 to 20 characters buys more entropy than sprinkling in a symbol.
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