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Passphrase Strength Calculator

Score a diceware passphrase in bits, using the EFF 7776-word list at 12.925 bits per word, and see its crack time.

About Passphrase Strength Calculator

A passphrase is a random draw with replacement from a known wordlist, so its entropy is the number of words times the bits per word — and the attacker is assumed to know the wordlist. Six EFF words give 77.5 bits, which beats a 12-character random alphanumeric password while staying typeable from memory. Passphrases are the only construction that reaches 80+ bits and still survives contact with a human being, so knowing the bits per word tells you exactly how many words your standard should demand.

Formulas

Passphrase Strength

entropy = words × log2(wordlist size), plus 1 bit per randomly capitalised word, plus 3.322 bits per random digit.

wordlist size
How many words the generator could have picked from
log2(7776)
12.925 bits — the EFF long list

Offline crack time

crack time = 2^entropy ÷ (2 × 10^11 guesses per second) for an MD5 hash on one 8-GPU rig.

Worked example

With the default values below, Passphrase Strength Calculator returns Passphrase Entropy of 77.55. Change any input above and every figure here is recalculated in your browser.

Inputs used

Number of wordsaccepts 1–24 words
6 words
Wordlistone of EFF short list — 1296 words, Diceware / EFF long list — 7776 words, Extended list — 20000 words, Large dictionary — 100000 words
Diceware / EFF long list — 7776 words
Random digit between words
No
Randomly capitalise each word
No
Random digits appendedaccepts 0–32 digits
0 digits

Results

Passphrase Entropy
77.55 bits
Entropy per Word
12.925 bits
Equivalent Random ASCII Characters
11.8 characters
Crack Time at 100 G guesses/s
3.505 × 10⁴ years
Crack Time (MD5, 8-GPU rig)
35,051 years

Step by step

  1. 1Values used
  2. 2Passphrase Strength
  3. 3Offline crack time
  4. 4Passphrase Entropy= 77.55 bits
  5. 5Entropy per Word= 12.925 bits
  6. 6Equivalent Random ASCII Characters= 11.8 characters
  7. 7Crack Time at 100 G guesses/s= 35,051.040 years
  8. 8Crack Time (MD5, 8-GPU rig)= 35,051 years

Assumptions and limits

  • The result is derived only from the 5 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 Passphrase Strength calculated?

entropy = words × log2(wordlist size), plus 1 bit per randomly capitalised word, plus 3.322 bits per random digit. A passphrase is a random draw with replacement from a known wordlist, so its entropy is the number of words times the bits per word — and the attacker is assumed to know the wordlist. Six EFF words give 77.5 bits, which beats a 12-character random alphanumeric password while staying typeable from memory.

Why does Passphrase Strength matter?

Passphrases are the only construction that reaches 80+ bits and still survives contact with a human being, so knowing the bits per word tells you exactly how many words your standard should demand.

What values do I need to enter?

This calculator takes 5 inputs: Number of words, Wordlist, Random digit between words, Randomly capitalise each word, Random digits appended. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Does using a well-known wordlist weaken the passphrase?

No. Kerckhoffs's principle applies: the strength is in the random selection, not the secrecy of the list. The maths above already assumes the attacker has the list and is guessing word combinations, not characters.

How many words do I need?

Four words is 51.7 bits and falls to a determined offline attack. Six words is 77.5 bits and is the usual recommendation. Eight words is 103.4 bits, appropriate for a password-manager master password or a disk-encryption key.

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