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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.

Inputs

characters

95 is every printable ASCII character: 26 + 26 + 10 digits + 33 symbols and space.

Password Entropy

105.1bits

Entropy per Character

6.570bits

Total Keyspace

4.401 × 10³¹

charset^length — every password of this shape

Strength Band

Strong — 80+ bits, safe against offline GPU cracking

Step by step

  1. Values used

    Password length = 16 characters; Character set = Printable ASCII (95)

  2. Password Entropy Score

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

  3. 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.

  4. Password Entropy

    = 105.1 bits

  5. Entropy per Character

    = 6.570 bits

  6. Total Keyspace

    = 44,012,666,865,176,570,000,000,000,000,000.000

  7. Strength Band

    = Strong — 80+ bits, safe against offline GPU cracking

How it works

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.

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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