Coin Tosses

Learn how flipping a coin 128 times generates real entropy for a seed phrase.

This browser tool is for education only. It does use cryptographically secure random functions to flip the coins, but it shouldn't be trusted. Your seed phrase should be generated by you, doing physical coin flips. Use the worksheet and the wordlist to do it for real.

Print worksheet

Why a coin?

A physical coin flip is genuinely unpredictable. the outcome depends on tiny variations in force, spin, and air resistance that no one controls.

Each BIP-39 word is picked from a list of 2048 words, and 211 = 2048, so it takes exactly 11 coin flips (11 bits) to pick one word.

To start, click the coin to flip it!

0 / 128 entropy bits flipped

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Bits → decimal

Each word's 11 coin-flip bits are read as a binary number: give each bit a place value (1024, 512, … 1) and add up the ones that are 1.

That gives a value from 0 to 2047 — the index used to look up the word in the wordlist.

Read the BIP-39 spec →

Binary → decimal transformer

Seed word list

This list fills in top-to-bottom as each word's bits finish decoding.

All 12 words together, in order, form your BIP-39 recovery seed phrase.

Seed Word list

Word 1 ·····
Word 2 ·····
Word 3 ·····
Word 4 ·····
Word 5 ·····
Word 6 ·····
Word 7 ·····
Word 8 ·····
Word 9 ·····
Word 10 ·····
Word 11 ·····

The BIP-39 wordlist

BIP-39 defines a fixed list of 2048 English words, each tied to a specific number from 0 to 2047, identical across every compliant wallet.

Looking up a word is just indexing into that list with the decimal number from your 11 bits.

Wordlist lookup

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