How this calculator works
For ordered strings with repetition, each position has the same number of choices. Without repetition, the available alphabet shrinks after every position. The count uses exact integer arithmetic. The entropy shown is log base two of the number of possibilities and describes uniform random selection across the entire space. Human choices, leaked patterns and extra composition requirements can make actual uncertainty much smaller. Custom alphabets count Unicode code points, so a displayed grapheme may contain multiple counted characters.
Formula
With repetition: count = A^L and ideal entropy = L log2(A). Without repetition: count = A!/(A - L)!, with entropy = sum from i = 0 to L - 1 of log2(A - i).
Worked example
Four positions chosen from ten digits allow 10^4 = 10,000 strings, including leading zeroes, with ideal entropy about 13.2877 bits. Two positions from four characters without repetition allow 4 × 3 = 12 strings.
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Frequently asked questions
Does the calculator generate passwords?
No. It counts a possible string space from the stated rules.
Are aabc four distinct characters?
No. The custom alphabet contains three distinct code points: a, b and c.
Does this entropy rate an existing password?
No. It assumes uniform selection from the modelled possibilities. It does not measure how a person or attacker would choose strings.