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Keyspace Size Calculator

Work out keyspace size instantly with clear inputs, formula shown and shareable results.

About Keyspace Size Calculator

Keyspace is the count of distinct values a secret can take: C^L for a string of length L over an alphabet of size C. Expressed in bits, entropy is L x log2(C), which is the number to compare against key lengths — a 12-character alphanumeric password carries about 71 bits, noticeably weaker than a 128-bit AES key.

Formula

Keyspace and entropy

keyspace = C^L; entropy bits = L x log2(C)

Worked example

With the default values below, Keyspace Size Calculator returns Total possible values of 10^21.51. Change any input above and every figure here is recalculated in your browser.

Inputs used

Character setone of Digits only (10), Lowercase letters (26), Letters, mixed case (52), Alphanumeric, mixed case (62), Full printable ASCII (95)
Alphanumeric, mixed case (62)
Lengthaccepts 1–128
12

Results

Total possible values
10^21.51
Entropy
71.45 bits
Characters in the set
62
Equivalent symmetric key length
71 bits

Step by step

  1. 1Values used
  2. 2Keyspace and entropy
  3. 3Total possible values= 10^21.51
  4. 4Entropy= 71.45 bits
  5. 5Characters in the set= 62
  6. 6Equivalent symmetric key length= 71 bits

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is entropy measured in bits?

Bits let you compare secrets of different alphabets directly and map them onto cryptographic key strength, where each extra bit doubles the search effort.

Does adding symbols help much?

Going from 62 to 95 characters adds only about 0.62 bits per character. Adding two more characters of length usually beats adding symbol complexity, and is easier to remember.

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