What Is Password Entropy?
Password entropy measures how unpredictable a password is. It is expressed in bits and calculated using logarithmic math.
If you want to calculate password strength accurately, understanding entropy is essential.
How Is Password Entropy Calculated?
Character Pool Size
The more possible characters available, the higher the entropy. Example pools:
- 26 lowercase letters
- 52 mixed case letters
- 94 printable ASCII characters
Password Length
Entropy increases linearly with length but exponentially in total combinations. Formula: Entropy = log2(characterPool^length)
How Many Bits Make a Strong Password?
- 80 bits – Recommended minimum
- 100+ bits – Extremely strong
Not sure whether to use a password or passphrase? Read our comparison guide on password vs passphrase security.
Entropy Chart Examples
| Length | Character Set | Approx Bits |
|---|---|---|
| 12 | Lowercase | 56 bits |
| 16 | Full ASCII | 105 bits |
| 20 | Full ASCII | 131 bits |
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FAQ
What is password entropy?
Password entropy measures how unpredictable a password is. It is expressed in bits and indicates resistance against brute force attacks.
Is 80 bits of entropy enough?
Yes. 80 bits of entropy is widely considered strong for modern security needs. Higher values (100+ bits) provide extremely strong protection.
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