Seed Phrase Entropy Calculator

A seed phrase, or mnemonic, is a human-readable backup of a cryptographic wallet seed. The BIP-39 standard encodes random entropy as a sequence of words drawn from a fixed 2,048-word list. Each word represents 11 bits because 2 to the power 11 equals 2,048. The phrase plus an optional passphrase reconstructs the wallet's master key.

Entropy in bits equals the word count multiplied by the base-2 logarithm of the wordlist size. For a BIP-39 12-word phrase from a 2,048-word list, that is 12 times log2(2,048), which is 12 times 11, equals 132 bits. BIP-39 reserves part of those bits as a checksum, so a 12-word phrase carries 128 bits of true entropy plus a 4-bit checksum.

A 24-word BIP-39 phrase carries 256 bits of entropy plus an 8-bit checksum, for 264 total bits across the words. This is why hardware wallets default to 24 words for maximum security. A 12-word phrase carries 128 bits, which is still considered strong.

It reports total bits across the words, which is word count times log2 of the wordlist. BIP-39 then dedicates a fraction of those bits to a checksum: roughly one checksum bit per 32 bits of entropy. Use the total bits figure for raw guessing resistance and subtract the checksum for true entropy if you are following BIP-39 exactly.

Each word's contribution is log2 of the list size, so a larger list packs more bits per word. The standard BIP-39 list is 2,048 words for exactly 11 bits each, which keeps the math clean and the phrase short. If you use a non-standard list, enter its size to get the correct per-word entropy.