Hash Generator
Generate cryptographic hashes of text, computed in your browser.
Developer Tools
Use tool
Password Entropy Calculator
Bits of entropy and brute-force time, from the maths.
Password Entropy Calculator tool
For the first option.
For the passphrase option.
The Diceware list has 7,776 words.
—
Entropy
—
Possible combinations
—
Average time to crack
—
Strength
—
Pool size
| Attacker | Guesses per second | Average time to crack |
|---|
Entropy measures the size of the search space, which is only the right model for a password chosen at random. A memorable password built from words, dates or substitutions has far less effective entropy than its length suggests, because a real attacker guesses patterns before it guesses randomly.
About the Password Entropy Calculator
Password Entropy Calculator measures the size of the search space a password sits in, expressed in bits. Each bit doubles the number of possibilities, so 50 bits is a thousand times harder to search than 40. The figure comes from the length and the number of options per position: twelve characters from a 62-character pool is 62 to the twelfth, or about 71.5 bits.
The passphrase mode uses the same formula with words as the unit. Four words drawn at random from the 7,776-word Diceware list give 51.7 bits, which is comfortably stronger than most hand-made passwords and far easier to remember. Six words reach 77.5 bits and are beyond any realistic brute-force attack.
One caveat matters more than all the arithmetic: entropy only describes a password chosen at random. A password built from a name, a date, a keyboard pattern or letter-for-symbol substitutions has a mathematical entropy that is simply wrong, because an attacker tries patterns first and reaches it in a tiny fraction of the search space. The crack times here are an upper bound for random passwords and a fantasy for memorable ones.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
Looking for something this does not cover? FreeToolsHub.org is another hub of free online tools that need no account, and it is worth a look if password entropy calculator is only part of what you are working on.
How to use the Password Entropy Calculator
- Choose work from and attacker guesses per secondThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
- Enter password length, number of words and words in the listDecimals are fine, and thousands separators are accepted and ignored.
- Read the entropy, possible combinations and average time to crackThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.
Features
- Shows entropy, possible combinations, average time to crack, strength and pool size together, so you are not running it twice
- A results table you can read across
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The password entropy calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Checking whether a password policy produces strong passwords
- Comparing a passphrase against a shorter complex password
- Seeing how much another word or character adds
- Explaining why length beats complexity
Frequently asked questions
How many bits of entropy is enough?
Around 60 bits resists a determined offline attack on a slow hash; 80 or more is strong against anything realistic. Below 40 is weak.
Is a passphrase really as strong as a complex password?
Yes, when the words are chosen at random. Four random Diceware words beat most eight-character complex passwords and are far easier to remember.
Why does the hash matter?
A slow hash like bcrypt or Argon2 limits an attacker to tens of thousands of guesses a second instead of billions, which is worth about 15 bits of entropy.
Does this tell me if my password has been breached?
No. Entropy is pure mathematics. A high-entropy password that has appeared in a breach is worthless, so check a breach database separately.
Related tools
If the password entropy calculator is not quite what you need, these other free tools solve closely related problems, and there are 11 more in tech calculators.
UUID Generator
Generate cryptographically random UUIDs in bulk, with format options.
Developer Tools
Use tool
Binary Calculator
Binary arithmetic with decimal, hex and octal output.
Tech Calculators
Use tool
Byte Converter
Bytes to KB, MB, GB and the KiB/MiB/GiB family.
Tech Calculators
Use tool
Exponent Calculator
Powers, including negative and fractional exponents.
Math Calculators
Use tool
Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.