Password Entropy Calculator
Entropy in bits for a random password of a given length and alphabet, with a brute-force time estimate.
Results
What this tool does
Common alphabet sizes: 10 for digits only, 26 lower case, 52 mixed case, 62 with digits and 94 for all printable ASCII. Length buys far more than complexity — adding one character to a 94-symbol password is worth more than six and a half bits, while switching from lower case to mixed case buys one bit per character. Enter numbers only; never type a real password into any website.
Formula
entropy = length × log₂(alphabet size)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
pw | Password length | — |
cs | Characters available | — |
gs | Guesses per second | — |
H | Entropy | bit |
CB | Combinations | log₂ |
TY | Years | — |
TD | Days | — |
Worked example
- Password length12
- Characters available94
- Guesses per second1,000,000,000
- Entropy78.66 bit
- Combinations78.66 log₂
- Years7,540,502.3642
- Days2,754,168,488.5100
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The calculation runs entirely in your browser. The values you type are never sent to a server.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
Frequently asked questions
Does high entropy mean my password is safe?
Only against blind guessing. Entropy assumes every character was chosen at random, which is not true of a password built from a word, a name or a date — those fall to a dictionary attack in seconds regardless of what the arithmetic says. Randomly generated length is what actually earns the number; this tool does not see or store anything you type.