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Password Entropy Calculator

Calculates entropy in bits from length and character set, and shows how long a brute-force attack would take.

Security Nothing uploaded No sign-up Free, unlimited
Security tool
Enter your figures and press Calculate.
In short Password Entropy Calculator is a free online tool on inputtesthub.com that calculates entropy in bits from length and character set, and shows how long a brute-force attack would take. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Password Entropy Calculator

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Password Entropy Calculator

The Password Entropy Calculator calculates entropy in bits from length and character set, and shows how long a brute-force attack would take. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Understanding why length beats complexity.
  • Setting a minimum password policy with actual numbers.
  • Comparing a passphrase against a random string.

The maths behind it

This tool uses entropy = length × log₂(alphabet size), and average crack time = 2^(entropy−1) ÷ guesses per second. Every intermediate value is shown on screen, so the result can be checked by hand.

Explained in our guides

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Frequently asked questions

Is the Password Entropy Calculator free?
It is free, with no account, no trial and no daily cap. Every security tool on inputtesthub.com works the same way: open the page and use it.
Is the Password Entropy Calculator safe to use with private information?
No. The Password Entropy Calculator runs entirely in your browser using JavaScript. Because the work happens locally, the utility also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
What is the equation behind the Password Entropy Calculator?
It uses entropy = length × log₂(alphabet size), and average crack time = 2^(entropy−1) ÷ guesses per second. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What problem does the Password Entropy Calculator solve?
The most common reasons people reach for it: understanding why length beats complexity. Setting a minimum password policy with actual numbers. Comparing a passphrase against a random string. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is the number rounded?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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