# Password Entropy Calculator

> Calculate the entropy in bits of a randomly generated password or Diceware-style passphrase from its length and the size of the character set or word list.

Category: IT, networking & security · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/password-entropy-calculator

Entropy measures how many equally likely choices a random generator could have made: length × log₂(pool size). It applies to passwords picked at random, not to ones people make up.

Also called: Passphrase entropy calculator, Password bits calculator.

## Inputs
- Type (options: Random characters, Random words; default chars)
- Length (unit characters; default 12)
- Characters drawn from (options: Digits only (10), Lower-case letters (26), Lower case + digits (36), Upper + lower + digits (62), All printable ASCII (94), Custom pool size; default alnum)
- Characters in the pool (default 70)
- Number of words (default 6)
- Words in the list (default 7776)

## Results
- Entropy
- Bits per character or word
- Equally likely possibilities
- Same as random printable-ASCII characters

## Formula

```
Entropy (bits) = L × log₂ N;  Possibilities = N^L
```

Where:
- L: number of characters or words
- N: characters in the pool or words in the list

## Worked example
1. Pool: 26 + 26 + 10 = 62 characters; log₂ 62 = 5.9542 bits each.
2. 12 × 5.9542 = 71.45 bits.
3. 62¹² = 3.23 × 10²¹ possible passwords.

**Result:** A random 12-character password from upper and lower case letters and digits has 71.45 bits of entropy.

## What the result means

Each extra bit doubles the guesses needed. Compare the result with an attacker’s guess rate in the Password Brute-Force Time Calculator to see what it means in time.

## Assumptions and limits
- Every character or word is chosen independently and uniformly at random, as a password manager or dice do.
- Human-chosen passwords have far less entropy than their length suggests, because attackers guess common words and patterns first. This calculator does not rate a password you type.

## Questions

### Why not type my password in to check it?

Entropy belongs to the method that produced the password, not the string. “Password1!” uses four character types but is among the first guesses any cracker tries.

### Words or characters?

Six Diceware words (77.5 bits) beat 12 random alphanumerics (71.5 bits) and are much easier to type and remember.

## Related calculators
- [Password Brute-Force Time Calculator](https://calculators.geekmidst.com/calculators/password-brute-force-time-calculator)
- [Password Generator](https://calculators.geekmidst.com/calculators/password-generator)
- [PBKDF2 Runtime Calculator](https://calculators.geekmidst.com/calculators/pbkdf2-runtime-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/password-entropy-calculator