TECHNICAL_DOC // GENERAL / BYTES
BYTES
A byte is 8 bits — the fundamental unit of Bitcoin's data structures.
Every field in a transaction, block-header/">block header, script, or key is measured and specified in bytes.
Understanding byte sizes is essential for parsing raw Bitcoin data, calculating transaction
weight, and verifying protocol compliance.
BYTE_SIZES_IN_BITCOIN
COMMON BITCOIN DATA SIZES
1 byte = 8 bits = 2 hex characters = values 0x00–0xFF
Block header fields:
version: 4 bytes (uint32)
prev_blockhash: 32 bytes (SHA256d hash)
merkle_root: 32 bytes (SHA256d hash)
time: 4 bytes (uint32 unix timestamp)
bits: 4 bytes (compact difficulty target)
nonce: 4 bytes (uint32)
Total header: 80 bytes
Transaction fields:
version: 4 bytes
input count: 1–9 bytes (compact size)
txid ref: 32 bytes (per input)
vout index: 4 bytes (per input)
sequence: 4 bytes (per input)
value: 8 bytes (per output, satoshis)
locktime: 4 bytes
Keys and hashes:
private key: 32 bytes
public key: 33 bytes (compressed)
SHA256 hash: 32 bytes
RIPEMD160 hash: 20 bytes
Schnorr sig: 64 bytes
ECDSA sig: 71–72 bytes (DER encoded)
SEGWIT
SegWit introduced weight units (WU) to discount witness-data/">witness data. Fee calculations use virtual bytes (vbytes) rather than raw bytes.
Weight unit rules (BIP 141):
Non-witness bytes: weight = bytes × 4
Witness bytes: weight = bytes × 1
Virtual bytes:
vbytes = ceil(weight / 4)
Example — P2WPKH input:
41 non-witness bytes × 4 = 164 WU
107 witness bytes × 1 = 107 WU
Total input: 271 WU = ~68 vbytes
Max block: 4,000,000 WU = 1,000,000 vbytes (1 MB vbyte limit)
Typical block: ~1.5–2 MB actual bytes, ~1 MB vbytes
TERMINOLOGY_INDEX
Byte
8 bits. Represented as 2 hex digits (00–FF). The base unit of all Bitcoin data structures.
Weight Unit (WU)
SegWit's measurement: non-witness bytes count 4×, witness bytes count 1×. Block limit: 4,000,000 WU.
Virtual Byte (vbyte)
weight / 4. The unit used for fee rate calculation (sat/vbyte). 1 vbyte = 4 WU.
Octet
Formal synonym for byte (8 bits). Used in RFCs and protocol specifications.