# Password Strength (Entropy) Calculator

URL: https://speedycalculator.com/calculators/other/password-entropy/
Last updated: 2026-10-25

> The password entropy calculator estimates how strong a randomly generated password is, in bits, from its length and the size of the character set, and how long it would take to guess.

## Inputs

- Password length
- Character set
- Guesses per second

## Results

- Entropy
- Average time to crack

## Formula

```
Entropy (bits) = length × log₂(character set size)
Guesses = 2^entropy ÷ 2 on average
```

## Explanation

Every extra character multiplies the number of possibilities. Length matters more than adding symbols.

### How to use the Password Strength

- **Password length**
- **Character set**
- **Guesses per second**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

The number of possible passwords is the character set size raised to the length; entropy is its base-2 logarithm.

### Inputs explained

FieldWhat to enterPassword lengthA numberCharacter setChoose one: Digits only (10), Lowercase (26), Upper + lowercase (52), Letters + digits (62) …Guesses per secondA number

### What each result means

- **Entropy** = [Password length]×ln([Character set])÷ln(2)
- **Average time to crack** = 2^([Entropy] - 1)÷[Guesses per second]÷31557600

### Example values

How the main result changes when **Password length** changes and everything else stays at the example values above:

Password lengthEntropy (bits)745.910.568.81491.817.5114.721137.628183.5

## Worked example

Inputs — Password length: 14; Character set: All printable ASCII (94); Guesses per second: 10,000,000,000.

Results — **Entropy = 91.8 bits**; Average time to crack = 6,662,787,888.97 years.

## FAQ

**Does this apply to passwords I chose myself?**
No; human-chosen passwords are far weaker than their length suggests.

**What is best?**
Use a password manager to generate long random passwords, and enable two-factor authentication.

**What formula does the Password Strength use?**
Entropy (bits) = length × log₂(character set size).


## Sources

- [NIST SP 800-63B Digital Identity Guidelines](https://pages.nist.gov/800-63-3/sp800-63b.html)