Password Strength Calculator
From Bits to a Plain-Language Verdict
Entropy in bits is precise but not immediately intuitive. This calculator takes the same entropy calculation used for password analysis and maps it onto a four-tier rating — Weak, Fair, Good, or Strong — so the result reads as an actionable verdict rather than a raw number that still needs interpreting.
The Formula
Entropy (bits) = Length × log2(Charset Size)
Rating: <28 bits Weak, 28–35 Fair, 36–59 Good, 60+ Strong
Rating: <28 bits Weak, 28–35 Fair, 36–59 Good, 60+ Strong
Charset size sums the enabled character classes — 26 for lowercase, 26 for uppercase, 10 for digits, 32 for symbols — and the resulting entropy is checked against fixed thresholds to produce the rating.
Where This Matters
- Signup forms — giving users real-time feedback on password choices before they submit.
- Policy communication — translating a technical entropy requirement into a rating non-technical staff can act on.
- Personal password hygiene — quickly checking whether a password you're about to reuse is actually adequate.
Rating Thresholds
| Entropy range | Rating | Example configuration |
|---|---|---|
| Below 28 bits | Weak | 5-char lowercase-only password (~23.5 bits) |
| 28–35.9 bits | Fair | 6-char lowercase-only password (~28.2 bits) |
| 36–59.9 bits | Good | 8-char, upper+lower+digits (~47.6 bits) |
| 60+ bits | Strong | 12-char, all four classes (~78.7 bits) |
Example entropy values computed from Entropy = Length × log2(Charset Size).
How to Use This Calculator
- Enter the Password Length in characters.
- Check the character classes used: lowercase, uppercase, digits, and/or symbols.
- Select Calculate to get the strength rating and underlying entropy value.
Related Calculations
See the raw entropy figure alone with the Password Entropy Calculator, or convert the entropy into an estimated crack time with the Brute Force Attack Time Calculator.