How to generate a strong password (and what entropy means)

# What entropy actually measures

Password entropy is measured in bits. Each bit doubles the number of possibilities an attacker must try.

• 40 bits = ~1 trillion guesses. A single modern GPU cracks this in minutes.
• 60 bits = ~1 quintillion. A determined attacker might spend months.
• 80 bits = ~1.2 × 10²⁴. Out of reach for anyone without state resources.
• 128 bits = practically infinite. Used for encryption keys.

# The math

For a random password from a character set of size N with length L:

entropy = L × log₂(N)

Per-character entropy by character set:

| Set | Size | Bits/char |

|---|---|---|

| Digits | 10 | 3.32 |

| Lowercase letters | 26 | 4.70 |

| Alphanumeric (mixed case) | 62 | 5.95 |

| Full ASCII printable | 94 | 6.55 |

So a 12-character password pulled from mixed-case alphanumeric = 12 × 5.95 ≈ 71 bits. Solid.

A 4-digit PIN = 13.2 bits. Trivial.

# Why "complexity rules" lie

Most password rules are theater:

• "At least one uppercase, one number, one symbol" — the attacker knows this too. It shrinks the search space you bother testing.
• "Change every 90 days" — encourages predictable patterns (Spring2024!, Summer2024!).
• "No dictionary words" — but correct horse battery staple (xkcd's classic) is ~44 bits, stronger than most "complex" 8-character passwords.

What actually matters is unpredictability + length. Entropy doesn't care what the characters are, only how many equally-likely options exist.

# The xkcd passphrase trick

4 random words from a 2048-word dictionary = 4 × log₂(2048) = 44 bits.

6 random words = 66 bits. Close to unguessable, still easy to type.

<div class="callout callout-tip" role="note"><div class="callout-title">Tip</div><div class="callout-body"><p>The key word is <strong>random</strong>. If you pick the words from your favorite song, a novel, or a movie, you're not getting 44 bits — you're getting maybe 15 because the space of "memorable phrases" is tiny. Use a diceware list or a password manager.</p></div></div>

# Recommended by use

| Use case | Length | Character set | Notes |

|---|---|---|---|

| Website, low-value | 12 | Alphanumeric | ~71 bits |

| Website, high-value | 16 | Full ASCII | ~105 bits |

| Email / password manager master | 20+ | Full ASCII or 6-word passphrase | Critical; never reuse |

| Encryption key | 32+ | Full ASCII | 200+ bits |

# How our password generator works

Our password generator uses crypto.getRandomValues() — the browser's cryptographically secure random source. Every bit is generated locally; nothing is sent over the network.

You can customize length (8–128), character set (digits, lowercase, uppercase, symbols), and exclude ambiguous characters (1/l, 0/O) for typed-from-paper use cases.

# Check an existing password

Paste into our Password Strength Checker to see:

• Estimated entropy in bits
• Time to crack at various attacker budgets
• Specific weaknesses (dictionary words, keyboard patterns, common substitutions)

All computed locally. We literally cannot see your password.

# The only real advice

1. Use a password manager. Generate 20+ character random passwords for everything.

2. Make the master password a 6-word passphrase. Memorize that one.

3. Enable 2FA everywhere it's offered.

Everything else is detail.

# Related tools

• Password Generator
• Password Strength Checker
• Hash Generator — for understanding how passwords are stored