Mnemonic Checksum Bits For Word Count

Return the entropy and checksum bit counts prescribed for a valid BIP39 mnemonic word count.

Description

A BIP39 mnemonic encodes entropy plus a checksum using eleven bits per word-list index.

A BIP39 mnemonic encodes entropy plus a checksum using eleven bits per word-list index. The checksum bits are derived from the entropy and are not additional independently random secret bits.^{[1, 2]}

Return the entropy and checksum bit counts prescribed for a valid BIP39 mnemonic word count.

When to use Mnemonic Checksum Bits For Word Count

Use this tool to return the entropy and checksum bit counts prescribed for a valid BIP39 mnemonic word count.

Choose the text, counts, explicit reference time or format parameters requested by this tool. Follow the stated byte, epoch-time and randomness assumptions.

How to use Mnemonic Checksum Bits For Word Count and understand its results

Choose the text, counts, explicit reference time or format parameters requested by this tool. Follow the stated byte, epoch-time and randomness assumptions.
Enter wordCount using the field table and calculation rules, then run the tool.
Read entropyBits, checksumBits, encodedBits. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
wordCount	Mnemonic word count	integer; minimum: 12; maximum: 24	Required

Enter one of 12, 15, 18, 21 or 24 words as the wordCount. The tool validates that supported count and calculates the three bit totals. For example, 12 words correspond to 128 entropy bits plus 4 checksum bits, for 132 encoded bits. Other counts are input errors.

entropyBits = (wordCount/3) × 32; checksumBits = entropyBits/32; encodedBits = wordCount × 11

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
entropyBits	Entropy bit count	integer; minimum: 0; maximum: 9007199254740991
checksumBits	Checksum bit count	integer; minimum: 0; maximum: 9007199254740991
encodedBits	Total encoded bit count	integer; minimum: 0; maximum: 9007199254740991

json

{
  "input": {
    "wordCount": 12
  },
  "output": {
    "entropyBits": 128,
    "checksumBits": 4,
    "encodedBits": 132
  }
}

Limitations and assumptions

No mnemonic words, checksum, wallet seed or key are processed. A matching word count does not prove that a phrase uses a valid word list or has a valid checksum. This structural lookup does not measure a phrase's actual randomness.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Diceware Words to Entropy Bits: Calculate ideal word-passphrase entropy from independent uniform choices in a caller-supplied Diceware-style word list. For a complementary task, use BIP32 Path Depth Parser Check: Parse a BIP32 path with m or M root and apostrophe-marked hardened indices, enforcing depth and public-derivation restrictions.

Further background: BIP 39: mnemonic entropy and checksum lengths.

References

Mnemonic Checksum Bits For Word Count — tool.io
BIP 39: mnemonic entropy and checksum lengths — Bitcoin Improvement Proposals

Similar or alternative tools

Diceware Words to Entropy Bits
Calculate ideal word-passphrase entropy from independent uniform choices in a caller-supplied Diceware-style word list.
BIP32 Path Depth Parser Check
Parse a BIP32 path with m or M root and apostrophe-marked hardened indices, enforcing depth and public-derivation restrictions.