Online Tool Store
Password Entropy Calculator
Calculate a password's entropy in bits and an estimated offline crack time from its character set and length. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Nothing you type here is sent anywhere — calculated entirely in your browser.
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bits of entropy
- Character set size
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- Length
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- Time to crack (offline, fast GPU)
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How it works
- Type or paste a password.
- The character set size and length determine the entropy in bits.
- See an estimated crack time and strength rating.
The formula
Entropy (bits) = length × log₂(character set size)
Character set size = 26 (lowercase) + 26 (uppercase) + 10 (digits) + 33 (symbols), whichever are used
Time to crack ≈ 2^entropy ÷ 2 ÷ guesses per second
FAQ
What is password entropy?
A measure, in bits, of how unpredictable a password is — calculated from the character set it draws from and its length. Each additional bit doubles the number of possible passwords an attacker would need to try, so entropy is the standard way to compare password strength mathematically.
How is the "time to crack" estimated?
It assumes a fast offline attack at roughly 10 billion guesses per second (a common benchmark for GPU-accelerated cracking against a weak or unsalted hash), and estimates the average case at half the total keyspace — a rough guide, not a guarantee, since real attack speed varies enormously by hashing algorithm.
How is this different from the Password Strength Checker tool?
This tool focuses purely on the mathematical entropy calculation and estimated crack time. The Password Strength Checker also flags weak patterns (common words, keyboard sequences, repeated characters) that pure entropy math doesn't catch.
Is my password uploaded anywhere?
No — every calculation happens locally in your browser as you type. Nothing is sent to a server.
How we compare
| Feature | Online Tool Store | Password manager strength meters | Manual entropy math |
|---|---|---|---|
| Shows the actual entropy number and formula | ✓ | Usually just a colored bar | ✓ |
| No account or app install | ✓ | Requires a password manager | ✓ |
For understanding the actual math behind a strength rating rather than trusting a colored bar, this shows the real numbers.