Tool
What the Password Entropy Calculator does
Password Entropy Calculator: calculates Entropy from Password. Example: password Tr0ub4dour&3 gives entropy 79 bits.
Entropy, derived from Password. Results refresh instantly, so trying variations costs nothing but a moment.
Length buys far more protection than complexity rules ever did. That is usually what brings developers generating credentials here.
Your data stays on your machine. Once the page has loaded you could disconnect entirely and it would still work.
If you want to check the arithmetic, the field table, the method and a worked example are further down.
What do the Password Entropy Calculator fields mean?
The Password Entropy Calculator uses 1 input. A complete set of starting values is loaded for you, so nothing is required before the first result appears.
| Field | What to enter | Default |
|---|---|---|
| Password | required | Tr0ub4dour&3 |
How does the Password Entropy Calculator work?
Each output is derived from the inputs above in a single pass; there is no hidden state carried between runs, so the same inputs always give the same calculation.
The tool refuses to guess: if a value is missing or impossible, it says so.
Worked example
These are the values the Password Entropy Calculator loads by default, and the result it produces from them. This walkthrough uses the starting values, which means you can follow along without typing anything.
| Password | Tr0ub4dour&3 |
|---|
| Entropy | 79 bits |
|---|
The entropy formula, worked through
Entropy in bits is E = L × log₂(R): L is the password’s length, R is the size of the character pool it draws from. Each additional bit doubles, on average, the number of guesses an attacker needs to find the password.
| Digits only | R = 10 | 3.32 bits/char |
|---|---|---|
| Lowercase only | R = 26 | 4.70 bits/char |
| Upper + lower | R = 52 | 5.70 bits/char |
| Alphanumeric | R = 62 | 5.95 bits/char |
| Alphanumeric + symbols | R = 95 | 6.57 bits/char |
Worth knowing
- Going from lowercase-only to the full 95-character set adds under 2 bits per character. Adding one more character of plain lowercase adds 4.7 bits. Length is the variable that actually moves the number.
- The formula assumes every character is chosen independently and uniformly: true of a machine-generated password, false of almost anything a person composes from memory.
- 2^E is the size of the space an attacker actually has to search for E bits of entropy; on average, brute force finds the answer after checking about half of it.
- This calculator and the strength checker above use the exact same underlying formula. The difference is purely which angle the page leads with: a practical verdict here, the arithmetic there.
Read next: What Actually Makes a Password Strong
How to use it
- Fill in Password.
- Type a value and the answer is already there by the time you stop.
- The panel reports Entropy.
- Share the link rather than a screenshot. It carries the values with it.
What this tool does not do
- Anything generated here is only as safe as where you store it afterwards.
- Anything generated here is only as safe as wherever you store it afterwards.
- It cannot flag an input that is technically valid but wrong for your case.
Frequently asked questions
Password, nothing else. Each field is pre-filled with a sensible default, meaning you can explore the calculation before committing to real figures.
With the values loaded when the page opens, entropy comes out as 79 bits. Change a value and the number is recomputed on the spot.
Nothing is logged. The tool is client-side code; your data stays where you entered it.
It is free to use, with no premium tier holding back the useful parts.
The logic is straightforward and testable; the worked example above uses the tool’s own defaults so you can verify it yourself.