What Is a Password Strength Calculator?
This calculator estimates how hard a password would be to guess, using its length and the types of characters it uses — without ever asking you to type an actual password. That's a deliberate choice: a strength estimator has no reason to see or store real credentials.
The result is expressed in bits of entropy (a measure of randomness) and an estimated brute-force crack time under a few realistic attack scenarios.
How to Read Your Results
Entropy (bits)
Entropy measures how many guesses an attacker would need in the worst case. Each additional bit doubles the number of possible passwords, so entropy grows fast with length.
Estimated Crack Time
An estimate of how long a brute-force attack would take on average, based on the attack speed scenario selected. Real-world attacks often succeed faster using dictionaries or known-password lists rather than pure brute force — this number is a ceiling, not a guarantee.
Strength Rating
A simple label based on entropy: under 36 bits is very weak, 36-60 is weak, 60-80 is reasonable, 80-100 is strong, and above 100 is very strong for most purposes.
Real-World Example
A 12-character password using lowercase, uppercase and digits (62 possible characters per position):
| Metric | Value |
|---|---|
| Entropy | ≈71.4 bits |
| Character set size | 62 |
| Crack time (fast GPU attack) | ≈4,900 years |
Adding symbols to the same 12-character password raises the character set to 94, pushing entropy above 78 bits — meaningfully stronger for the same length.
Tips for Stronger Passwords
- Length beats complexity. A 16-character password with only lowercase letters often beats a 10-character password with every character type.
- Use a password manager to generate and store long, unique passwords for every site.
- Avoid dictionary words and personal information — this calculator assumes random selection, which real passwords often aren't.
- Enable multi-factor authentication wherever it's offered; it protects you even if a password is compromised.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team