The bits field

What it is

The bits field is part of every Bitcoin block header. It encodes the network's target difficulty for that block — the threshold a block hash must beat to be considered valid by consensus. Every node verifies it, every block has it, and its value is set deterministically by Bitcoin's difficulty-retarget rules. It is a 4-byte field, represented as 8 hexadecimal characters in standard tooling.

Encoding

bits is a compact 4-byte representation of a 256-bit target. The structure is 1 byte of exponent followed by 3 bytes of mantissa (coefficient).

The decoded difficulty target is computed as:

target = mantissa × 2^(8 × (exponent − 3))

DMT does not use the decoded target. It references the integer value of the raw 4-byte field itself — i.e. the bits value parsed as a single big-endian unsigned integer.

bits     0x1703a30c
exp      0x17 (23)
coeff    0x03a30c (238860)
integer  385948428

Why DMT picks this field

The bits field changes only at difficulty retargets — once every 2,016 blocks, roughly every two weeks. Between retargets, bits is constant; at each retarget, it adjusts to track network hashrate. As difficulty rises, the integer encoding of bits falls, and as difficulty falls, the integer rises.

This makes the bits value a slow-moving function of Bitcoin's actual security: a per-block number that everyone agrees on, that no one chose, and that loosely tracks the chain's own physics. A supply curve anchored to bits declines as the network grows — mirroring the spirit (if not the math) of Bitcoin's halving cadence.

Range

Per the Bitcoin protocol, bits values have historically spanned roughly 0x17000000 to 0x1d00ffff. The integer encoding is therefore non-uniform across the chain's history, often producing per-block mint quantities in the tens of millions.

In the DMT element registry

DMT's element registry assigns numbered fields to keys in Bitcoin's block JSON. Field 11 is bits. The element name dmt.11.element represents the whole-field reference; this is the element identifier a $BIT mint inscription points at. Element-name conventions and the full registry are defined by the DMT specification.

Verification

Anyone can independently decode the bits field of any Bitcoin block. Standard sources include a local Bitcoin Core node (getblockheader <hash>), any block explorer, and the raw block hex. Because bits is part of the block header, it is covered by Bitcoin's own consensus and proof-of-work — it cannot be altered without re-mining the block.

The mint quantity for any given block is therefore deterministic and verifiable from chain data alone, with no reliance on an indexer's good behavior.