Diceware Passphrase Entropy Calculator | See How Strong Your Word Count Really Is

Estimate the entropy of a Diceware passphrase from four word lists — Diceware and EFF Large (7776), EFF Short (1296), and BIP-39 (2048) — and a length of 1 to 20 words. Get entropy in bits, total combinations, brute-force time, and a strength rank benchmarked against the NIST SP 800-63B 80-bit guidance.

💡 Stop guessing your word count

"Six words is enough" gets repeated everywhere, but the honest answer depends on your word list and your threat model. This calculator turns that debate into numbers: pick a list, drag the word count, and watch the entropy, crack time, and strength rank update together.

Each word from a 7776-word list adds about 12.9 bits, so six words land at roughly 77.5 bits and seven at about 90.4 bits. Because entropy scales linearly with word count, nudging the slider by one word shows you exactly how much margin a single extra word buys — and where you cross the line from "Strong" into "Very strong."

The attack-speed selector spans four realistic scenarios, from a throttled online login (100 guesses/sec) to an offline GPU rig hammering fast hashes (1 trillion/sec). The same six-word phrase can survive for millennia against one attacker and fall in years against another, and seeing both side by side is the point. The random-string equivalents — alphanumeric and printable ASCII — also let you compare a memorable passphrase against the character-soup password it would replace.

🧐 Frequently Asked Questions

Diceware vs EFF vs BIP-39 — what changes? The list size. The original Diceware list and EFF Large both hold 7776 words (6⁵); EFF Short holds 1296 (6⁴); BIP-39 holds 2048 (2¹¹). More words means more bits per word. EFF's words also average 7.0 characters versus Diceware's 4.3, trading a little length for fewer typos and clearer spelling.

Is six words actually enough? With a 7776-word list, six words gives about 77.5 bits. Diceware author Arnold Reinhold raised his recommendation from five to six words back in 2014. For high-value or long-lived secrets, seven words or more is the safer call. NIST SP 800-63B points to roughly 80 bits as the bar for strong passphrases, which is exactly where this tool flips the rank to "Very strong."

What is the custom dictionary size for? For any list outside the presets — a non-English Diceware list, a self-rolled wordlist, or a niche scheme. Enter the vocabulary count directly (2 to 1,000,000) and the bits-per-word recalculate for that list.

Why does crack time read in centuries or millennia? It is the average time to search half the keyspace at your chosen attack rate. Once entropy clears 80 bits, even a trillion guesses per second runs past the age of the universe — a practical "uncrackable" signal. The estimate assumes a true random Diceware roll with no proper nouns or known phrases baked in.

📚 Why a passphrase beats a tangled password

Security folklore long pushed gnarly strings like J7$kq!2pZ as the gold standard, but those are painful to type and easy to forget — so people reuse them. Diceware flips the trade-off: a six-word phrase like a string of unrelated dictionary words is dramatically easier to remember yet carries more entropy than a random 12-character password drawn from the full 94-character ASCII set.

The reason is simple arithmetic. Twelve printable-ASCII characters give about 78.6 bits, while six Diceware words give about 77.5 — practically a tie, except the words sit in your memory and the symbol soup does not. That's why the random-string equivalents in this tool are worth a glance: they show the character-count password you'd need to match the phrase you already find easy to recall.