Password Strength Calculator
Check how strong your password is by analyzing length and character variety.
What Is a Password Strength Calculator?
A password strength calculator analyzes how difficult your password would be for an attacker to crack. It looks at your password’s length and the variety of characters it uses, then calculates an entropy score — a measure of unpredictability. The higher the entropy, the stronger the password. This tool gives you a clear strength rating and an estimate of how long it might take to crack.
How to Use This Password Strength Calculator
Using the tool is simple:
- Type your password into the field. A live strength bar updates as you type.
- Click Check Strength for a full analysis.
- View your strength rating, entropy score, estimated charset size, and estimated time to crack.
Your password is analyzed entirely in your browser and is never transmitted or stored.
The Formula Behind the Password Strength Calculator
The tool estimates the number of possible characters your password could use (the charset) and computes entropy using this formula:
Entropy (bits) = Length × log₂(Charset size)
The charset size depends on the types of characters present:
| Character Type | Count |
|---|---|
| Lowercase letters (a–z) | 26 |
| Uppercase letters (A–Z) | 26 |
| Digits (0–9) | 10 |
| Symbols (e.g. !@#$) | 33 |
Entropy is then mapped to a strength rating:
| Entropy | Rating |
|---|---|
| < 30 bits | Very Weak |
| 30–44 bits | Weak |
| 45–59 bits | Fair |
| 60–79 bits | Strong |
| ≥ 80 bits | Very Strong |
Example Calculation
Consider the password “Tr0ub4dor&2026”, which is 14 characters long and uses lowercase, uppercase, digits, and symbols:
- Charset: 26 + 26 + 10 + 33 = 95 possible characters
- Entropy: 14 × log₂(95) = 14 × 6.57 = 91.98 bits
| Metric | Value |
|---|---|
| Length | 14 characters |
| Charset size | 95 |
| Entropy | 91.98 bits |
| Rating | Very Strong |
Why Password Strength Matters
Weak passwords are a leading cause of account compromise. Attackers use automated tools that try millions of combinations per second, and passwords based on common words, names, or short lengths can be cracked almost instantly. A strong password — long, with a mix of character types, and not reused across accounts — dramatically raises the effort required to break in and protects your personal and financial data.
How This Password Strength Calculator Works
When you click Check Strength, the tool examines your password’s length and which character types it contains. It adds up the size of the possible character set, then multiplies the length by the base-2 logarithm of that set size to compute entropy in bits. This value is converted to a rating and color, and used to estimate how long an offline attack running one billion guesses per second would take. Everything happens locally in your browser — your password never leaves your device.
Frequently Asked Questions
What is password entropy?
Entropy measures the unpredictability of a password in bits. Each bit doubles the number of possible combinations, so higher entropy means exponentially more guesses are needed to crack it.
How long should my password be?
Aim for at least 12 characters, and ideally 16 or more. Longer passwords are more important than complexity alone because every added character multiplies the number of combinations.
Is a long password with only lowercase letters strong enough?
Length is powerful. A 20-character lowercase password has about 94 bits of entropy, which is strong, though adding a few special characters makes it even more resilient.
Does this calculator store my password?
No. The analysis runs entirely in your browser using JavaScript. Nothing is sent to a server or saved anywhere.
Should I use the same strong password for everything?
No. If one site is compromised, reuse puts all your accounts at risk. Use a unique strong password per account, ideally managed with a password manager.