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.
Inputs
The EFF long list holds 7776 = 6^5 words, so five dice rolls pick one word and each word is worth log2(7776) = 12.925 bits.
Passphrase Entropy
77.55bits
Entropy per Word
12.925bits
Equivalent Random ASCII Characters
11.8characters
Crack Time at 100 G guesses/s
3.505 × 10⁴years
Crack Time (MD5, 8-GPU rig)
35,051 years
Step by step
Values used
Number of words = 6 words; Wordlist = Diceware / EFF long list — 7776 words; Random digit between words = No; Randomly capitalise each word = No; Random digits appended = 0 digits
Passphrase Strength
entropy = words × log2(wordlist size), plus 1 bit per randomly capitalised word, plus 3.322 bits per random digit.
Offline crack time
crack time = 2^entropy ÷ (2 × 10^11 guesses per second) for an MD5 hash on one 8-GPU rig.
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
= 35,051.040 years
Crack Time (MD5, 8-GPU rig)
= 35,051 years
How it works
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.
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.
You might also need
- Password Entropy Score CalculatorCommonly used together
- Password Crack Time CalculatorCommonly used together
- Dictionary Attack Probability CalculatorCommonly used together
- Authentication Health Score CalculatorAlso in Password Security
- MFA Security CalculatorAlso in Password Security
- Minimum Password Length CalculatorAlso in Password Security