Password Entropy and Cracking Time Calculator
See how hard a randomly generated password is to guess.
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Password Entropy and Cracking Time Calculator by TheCalcTools
How the Password Entropy and Cracking Time Calculator works
Choose the password length and the character set it is drawn from, then your assumed attack speed.
Entropy is length × log₂(character set size).
On average an attacker finds the password after trying half the possibilities.
The formula
Worked example
Using the default values shown in the calculator:
| Password length | 12 |
|---|---|
| Character set | All printable ASCII (94) |
| Guesses per second (billions) | 10 |
- Entropy = 12 × log₂(94) = 78.7 bits.
- There are about 4.76 × 10^23 possible passwords.
- At 10 billion guesses a second, the average time to crack is 754050.2 years.
Result:
| Entropy (bits) | 78.7 |
|---|---|
| Possible passwords | 4.76 × 10^23 |
| Average time to crack | 754050.2 years |
Frequently asked questions
Does this apply to passwords I choose myself?
No. These figures assume every character is chosen randomly. Human-chosen passwords follow patterns and are much easier to guess.
What length is enough?
Random passwords of 12–16 characters from a large set are strong against most attackers. A passphrase of 5–6 random words is similar.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.