BIP39 seed and secret key My understanding is that the 12-word seed is used to recover wallets' private keys. However, if each private key is 256-bits long, and the dictionary for the seed only contains 2048 words, then that's not nearly enough to cover them all: 2048^12 = 2^132 &lt;&lt; 2^256.

Where is my misunderstanding?
2048^12 = 2^132 &lt;&lt; 2^256


It doesn't need to be able to describe every private key. You always start with the mnemonic, never calculating a mnemonic from a private key.