Free Password Strength Calculator Online
Password entropy, strength score, crack time estimate and improvement tips
The Password Strength Calculator measures your password's entropy in bits, assigns a strength score from 0–100, and estimates how long it would take to crack using a brute-force attack at modern GPU speeds. Security professionals, IT policy writers, and anyone curious about whether their passwords actually stand up to attack will find the detailed breakdown useful.
Frequently Asked Questions
About the Password Strength
Password strength is not about how complex a password looks to a human — it's about entropy: the mathematical measure of how many possible combinations an attacker must try. A password that seems complex ("P@ssw0rd!") can be trivially cracked because attackers use rule-based mutation lists that already include common substitutions.
This calculator evaluates entropy based on character set size and length, checks for common patterns and dictionary words, and translates the result into an estimated crack time at realistic attack speeds (10 billion guesses/second for a dedicated GPU rig). The strength score accounts for both raw entropy and pattern vulnerabilities.
IT administrators use this to enforce evidence-based password policies — replacing arbitrary "must include a number" rules with minimum-entropy requirements. Individuals use it to understand which of their stored passwords are weakest and should be replaced first.
When Should You Use This?
The Password Strength is ideally suited for developers, network engineers, and IT professionals who need to perform quick, accurate calculations related to general calculations. Use this tool when you need to verify figures, compare different scenarios, or get a precise answer without manual computation errors.
What Does The Result Mean?
The calculated output provides an instant, accurate resolution to your input parameters. You can use these results directly for your planning, assignments, or professional tasks, knowing they are based on standardized formulas.
Example Calculation
Comparing two passwords of the same length
📥 Inputs
- Password A: "password123" (11 chars, lowercase + digits)
- Password B: "kR7@mP2#xL9" (11 chars, mixed case + digits + symbols)
🔢 Calculation Steps
- 1Password A character set: 26 lowercase + 10 digits = 36 characters
- 2Password A entropy: 11 × log₂(36) = 11 × 5.17 = 56.9 bits
- 3Password B character set: 26 + 26 + 10 + 32 symbols = 94 characters
- 4Password B entropy: 11 × log₂(94) = 11 × 6.55 = 72.1 bits
- 5Crack time at 10 billion guesses/sec: A ≈ 3.7 hours | B ≈ 62 years
Limitations of this Calculator
- Results are based purely on the mathematical relationship of the inputs provided.
- Does not account for edge cases or extreme outlier values that fall outside standard formula constraints.
- Calculated outputs should be double-checked against your specific real-world requirements before finalizing important decisions.
How to Use the Password Strength
- 1Enter your values into the Password Strength input fields above.
- 2Review the input labels to ensure you are using the correct units.
- 3Click the "Calculate" button to get your instant result.
- 4Use the step-by-step breakdown to understand how the result was calculated.
- 5Export or copy your result to use in reports or share with others.
Tips & Best Practices
- A 12-character password with mixed case, numbers and symbols would take centuries to crack by brute force.
- Double-check your input units before calculating — using the wrong unit is the most common source of errors.
- Bookmark this Password Strength for quick access next time you need it.
- Use the share button to send your results to a colleague or save them for later reference.
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