Passphrase Strength Calculator
Passphrase entropy bits, crack time, and rating from word count.
What it does
Word passphrases turn dice into defense. Each rolled word adds nearly thirteen bits of guessing work for attackers.
The tool above multiplies word counts out. Five words give 65 bits, or about 886 years at a billion guesses per second, rating strong. Counts are universal, so no unit toggle is needed.
Twelve ninety two fits standard lists. Seven thousand seven hundred seventy six words per list gives log base two of that per pick.
Ratings guide length. Under forty reads weak, sixty fair, eighty strong, with very strong above.
Rolling beats choosing. Favorite words cluster while dice spread evenly across the list.
How to use
- Enter word count: 5 suits the default.
- Read bits first.
- Read crack time next.
- Read rating.
- Roll words, never pick favorites.
Formula
- words
- Words rolled from the list.
Twelve point nine two bits per word suits 7776 word diceware lists. Attacker rate assumes a billion guesses per second.
Worked example
Example: 5 word passphrase
Defaults: 5 words. These are also the default values, so the page opens on this answer.
- Words: 5 diced words.
- Bits: 5 x 12.92 = 64.6, shown as 65 bits.
- Guesses: 2^64.6 at a billion per second.
- Time: about 886 years.
- Rating: 65 sits strong.
- Tool shows 65 bits, 886 years, Strong.
Reference table
| Words | Bits | Rating |
|---|---|---|
| 3 | 39 bits | Weak |
| 4 | 52 bits | Fair |
| 5 | 65 bits | Strong |
| 8 | 103 bits | Very strong |
Limits
- Math model only. Leaks beat entropy.
- Short lists cut real bits.
- Reuse across sites voids math.
- Quantum futures excluded.
Common mistakes
- Picking favorite words.
- Short lists assumed long.
- Reusing one phrase everywhere.
- Storing in plain text notes.
- Skipping two factor backup.
Try it yourself
Quick checks. Answers sit tucked under each question.
3 words?
Bits are 3 x 12.92 = 38.8, shown as 39 bits. Rating is Weak.
8 words?
Bits are 8 x 12.92 = 103.4, shown as 103 bits. Rating is Very strong.
Questions
Entropy of 5 words?
Multiply words by 12.92 bits. Here 5 x 12.92 = 65 bits after rounding.
Bits per word?
Near 12.92 bits each for 7776 word diceware lists.
Crack time?
Divide guesses by a billion per second. Here about 886 years.
Ratings?
Under 40 weak, 60 fair, 80 strong, above very strong. Here 65 is strong.
Word choice matter?
Yes. Reused words and short lists cut real entropy.
Math enough?
No. Storage and phishing beat math for most accounts.