Passphrase Entropy Calculator
Measure the true strength of a random word passphrase in bits, and see how long it would take to crack.
How it works
Entropy (bits) = words × log₂(list size) · Combinations = 2^bits · Avg crack time = 2^bits ÷ 2 ÷ guesses-per-second
A passphrase built from randomly chosen words has entropy equal to the number of words times the log base 2 of the word-list size — each word from a 7,776-word Diceware list adds about 12.9 bits. Entropy only counts if each word is chosen at random; picking a memorable phrase from a song or book adds far fewer bits than the word count suggests. Because an attacker on average finds the answer after trying half the space, the expected crack time is the full space divided by two, then divided by their guess rate.
Worked example
Six random Diceware words: log₂(7,776) ≈ 12.925 bits per word, so 6 × 12.925 ≈ 77.5 bits. That is 2^77.5 ≈ 1.7 × 10²³ possible passphrases; at a trillion guesses per second the average attack still runs for thousands of years.
Frequently asked questions
How many words make a strong passphrase?
With a 7,776-word list, four words give about 51 bits (adequate for low-value accounts), five give about 65 bits, and six give about 77 bits — enough to resist even a fast offline attack. Aim for at least 70–80 bits for anything important.
Does adding numbers or symbols help?
Only if they are random. A random symbol from a 30-character set adds about 4.9 bits — less than one extra word. Adding a word is usually easier to remember and adds more entropy.
Is a passphrase better than a random password?
For the same entropy they are equally strong, but passphrases are far easier for people to remember and type, which is why word-based schemes like Diceware are popular for master passwords.
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This calculator is for educational purposes. Double-check important results before acting on them.