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Password Entropy Score Calculator

Score password entropy in bits from its length and character set, with the full keyspace and a strength band.

About Password Entropy Score Calculator

Entropy measures how many equally likely possibilities an attacker must search. Each extra character multiplies the keyspace by the charset size, which adds a constant log2(charset) bits — 6.57 bits per character for printable ASCII. The figure is only honest for genuinely random passwords; a human-chosen password of the same shape carries far less real entropy. Bits of entropy is the one password metric that maps directly onto attacker work, so it is the number to put in a standard instead of vague rules about mixing symbols.

Formulas

Password Entropy Score

entropy (bits) = length × log2(charset size), and keyspace = charset size ^ length.

length
Number of characters in the password
charset size
Count of distinct characters the password could draw from

Bits per character by character set

log2(10) = 3.322 · log2(26) = 4.700 · log2(52) = 5.700 · log2(62) = 5.954 · log2(95) = 6.570 bits per character.

Worked example

With the default values below, Password Entropy Score Calculator returns Password Entropy of 105.1. Change any input above and every figure here is recalculated in your browser.

Inputs used

Password lengthaccepts 1–128 characters
16 characters
Character setone of Digits only (10), Lowercase letters (26), Mixed-case letters (52), Alphanumeric (62), Printable ASCII (95)
Printable ASCII (95)

Results

Password Entropy
105.1 bits
Entropy per Character
6.570 bits
Total Keyspacecharset^length — every password of this shape
4.401 × 10³¹
Strength Band
Strong — 80+ bits, safe against offline GPU cracking

Step by step

  1. 1Values used
  2. 2Password Entropy Score
  3. 3Bits per character by character set
  4. 4Password Entropy= 105.1 bits
  5. 5Entropy per Character= 6.570 bits
  6. 6Total Keyspace= 44,012,666,865,176,570,000,000,000,000,000.000
  7. 7Strength Band= Strong — 80+ bits, safe against offline GPU cracking

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 3 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

How is Password Entropy Score calculated?

entropy (bits) = length × log2(charset size), and keyspace = charset size ^ length. Entropy measures how many equally likely possibilities an attacker must search. Each extra character multiplies the keyspace by the charset size, which adds a constant log2(charset) bits — 6.57 bits per character for printable ASCII. The figure is only honest for genuinely random passwords; a human-chosen password of the same shape carries far less real entropy.

Why does Password Entropy Score matter?

Bits of entropy is the one password metric that maps directly onto attacker work, so it is the number to put in a standard instead of vague rules about mixing symbols.

What values do I need to enter?

This calculator takes 2 inputs: Password length, Character set. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

How many bits of entropy is enough?

60 bits survives an online attack but not an offline one against a fast hash. 80 bits is the practical floor for anything protecting money or administrative access. 128 bits matches a symmetric key and is what a password manager should generate by default.

Does adding a symbol help more than adding a character?

Adding one character to a 16-character alphanumeric password adds 5.95 bits. Switching that whole password from alphanumeric to printable ASCII adds only 16 × (6.570 − 5.954) = 9.9 bits. Length is the cheaper lever, which is why NIST SP 800-63B favours length over composition rules.

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