Definition
A virtual byte (vByte or vB) is the everyday unit Bitcoiners use to size transactions and price fees. It is defined simply as four weight units divided by four—that is, one vByte equals four weight units. Because a block holds 4,000,000 weight units, it equivalently holds 1,000,000 virtual bytes. Wallets and mempool explorers quote fee rates in satoshis per virtual byte (sat/vB), which is why the term appears every time you set a fee.
Why Not Just Use Bytes?
Before SegWit, transaction size was measured in raw bytes and fees were quoted in sat/byte. SegWit's witness discount broke that one-to-one relationship: a SegWit transaction's witness data counts less toward the block limit than its non-witness data. The virtual byte restores a single, fair number that reflects a transaction's true cost to the network. A transaction's virtual size (vsize) is its weight divided by four, rounded up.
Practical Fee Math
Suppose your transaction has a weight of 565 units. Its virtual size is 565 ÷ 4 ≈ 142 vB. At a fee rate of 20 sat/vB, you would pay roughly 2,840 satoshis. Choosing native SegWit (bech32) or Taproot addresses lowers vsize for the same logical spend, directly reducing what you pay. This is one of the simplest sovereignty levers available: better address types mean cheaper self-custody movements.
The virtual byte is derived directly from the weight unit, and the 1-million-vByte ceiling is enforced as a hard consensus limit alongside the other consensus rules every full node checks.
In Simple Terms
A virtual byte (vByte or vB) is the everyday unit Bitcoiners use to size transactions and price fees. It is defined simply as four weight…