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Password Entropy Calculator

Estimate password entropy from length, character pool, and attacker guess rate without entering the actual password.

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Inputs

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Results

Estimated Entropy
Character Pool94
Average Crack Time~1e15 years
Average Guesses~1e31

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Assumptions

  • Characters are assumed to be chosen uniformly at random from the selected pool.
  • This calculator does not check breached password lists or user-specific patterns.
  • No actual password is required or stored; calculations run locally.

Sensitivity preview

Password Length -10%: Estimated Entropy 94.39 bits

Password Length Current: Estimated Entropy 104.87 bits

Password Length +10%: Estimated Entropy 115.36 bits

Formula: Entropy bits = length * log2(character pool). Average guesses = 2^(entropy - 1). Average crack time = average guesses / guesses per second.

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About this Password Entropy Calculator

Entropy estimates how many possibilities an attacker must search. Longer passwords and larger character pools raise entropy, but real-world strength also depends on reuse, leaks, patterns, and storage security.

Who this calculator is for

  • Security teams explaining password policy tradeoffs.
  • Developers comparing generated password lengths.
  • Privacy-minded users who do not want to paste real passwords into a tool.

When to use it

  • Estimate entropy for generated passwords.
  • Compare length versus character set choices.
  • Convert an assumed guess rate into an approximate brute-force time.

How to use this calculator

  1. Enter password length.
  2. Select which character classes are allowed.
  3. Enter an assumed guesses-per-second rate.
  4. Review entropy bits, character pool size, and estimated average crack time.

Key assumptions

  • Characters are assumed to be chosen uniformly at random from the selected pool.
  • This calculator does not check breached password lists or user-specific patterns.
  • No actual password is required or stored; calculations run locally.

Accuracy and testing

Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.

View accuracy page

How this calculator works

Character pool = selected character set sizes. Entropy bits = Length x log2(pool size). Average guesses = 2^(entropy - 1). Average crack time = Average guesses / guesses per second.
Entropy bits = length * log2(character pool). Average guesses = 2^(entropy - 1). Average crack time = average guesses / guesses per second.

Inputs explained

Length

Number of characters in the password or generated secret.

Character classes

The possible symbols at each character position.

Guesses per second

An assumed offline or online attack rate. Real rates vary enormously.

Understanding your results

Higher entropy is stronger, but this is a mathematical estimate. Common words, reused passwords, leaked credentials, and predictable patterns can be much weaker than the estimate.

Example scenarios

Generated 16-character password

A 16-character password using upper, lower, numbers, and symbols has about 105 bits of entropy if characters are randomly chosen.

Key Features

  • Instant Calculation
  • Private & Secure
  • Mobile Optimized

Tips & Best Practices

  • Use a password manager to generate random unique passwords.
  • Do not reuse passwords across accounts.
  • For human-memorable secrets, consider longer passphrases generated from random words.

Frequently Asked Questions

Why not enter the actual password?
You do not need to. Entering length and character classes avoids exposing a real secret while still estimating mathematical entropy.
Does entropy guarantee password safety?
No. Reuse, phishing, malware, leaked hashes, weak hashing, and predictable patterns can defeat otherwise strong-looking passwords.
What guess rate should I use?
Online systems may allow very few guesses per second. Offline attacks against leaked hashes can be much faster. Use a conservative high number for worst-case planning.