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Password Entropy Calculator

Compute the exact Shannon entropy in bits for any password.

Best for: Comparing two password schemes, or justifying a minimum length policy.

Complete guide

Input

How it's calculated & sources
The Password Entropy Calculator uses the standard, deterministic formula, so the same inputs always produce the same result. It runs entirely in your browser, so your inputs are never uploaded. Last reviewed June 2026.

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

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Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is Password Entropy?
A password entropy calculator measures, in bits, how much randomness a password has — the single best indicator of how resistant it is to brute-force guessing.
Why does Password Entropy matter?
Each extra bit doubles the number of possibilities. Around 80 bits is strong for important accounts; passphrases reach that easily with a few random words.
How is Password Entropy calculated?
Entropy equals the password length multiplied by the log base 2 of the character-pool size. A bigger pool (adding uppercase, digits and symbols) adds a few bits per character; adding length adds the same bits for every extra character, which is why length is the most efficient way to get strong. Formula: Entropy (bits) = length x log2(pool size).
What are common password entropy mistakes?
Counting entropy from the pool while ignoring that a real password may use predictable words.
When should you use the Password Entropy Calculator?
Comparing two password schemes, or justifying a minimum length policy.

What is the Password Entropy Calculator?

A password entropy calculator measures, in bits, how much randomness a password has — the single best indicator of how resistant it is to brute-force guessing.

How the Password Entropy Calculator works

Entropy equals the password length multiplied by the log base 2 of the character-pool size. A bigger pool (adding uppercase, digits and symbols) adds a few bits per character; adding length adds the same bits for every extra character, which is why length is the most efficient way to get strong.

Entropy (bits) = length x log2(pool size)

Bits per character by pool

lowercase264.7
+ digits365.2
+ uppercase626.0
+ symbols946.6

Common mistakes to avoid

  • Counting entropy from the pool while ignoring that a real password may use predictable words.
  • Assuming complexity beats length — it usually does not.
  • Treating entropy as a guarantee rather than a resistance estimate.

Keywords: password, entropy, bits, shannon.

Sources: NIST SP 800-63B — Appendix A (password strength)

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the Password Entropy Calculator free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the Password Entropy Calculator?+

Password Entropy Calculator uses the standard password entropy formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The Password Entropy Calculator runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the Password Entropy Calculator on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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# Password Entropy Calculator — the free tool I keep coming back to

Compute the exact Shannon entropy in bits for any password.

Try it: https://freetoolsgalaxy.com/tools/password-entropy-calculator
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The fastest way is to use a free in-browser password entropy calculator: https://freetoolsgalaxy.com/tools/password-entropy-calculator. Compute the exact Shannon entropy in bits for any password.

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