What is Virtual byte (vB)?
The unit transaction size is measured in for fee purposes, equal to four weight units, introduced so SegWit data is discounted.
SegWit moved signature data into a separate witness section that counts for one weight unit per byte instead of four. A block holds four million weight units, equivalently one million virtual bytes.
This is why SegWit transactions are cheaper: the same economic action occupies fewer virtual bytes and therefore costs less at the same fee rate.
Related terms
SegWit
A 2017 soft fork that moved signature data into a separate witness structure, fixing transaction malleability…
Transactions & feesFee rate (sat/vB)
What a transaction pays per virtual byte of the space it occupies. Miners prioritise by fee rate, not by…
How it worksBlock
A batch of transactions accepted into the ledger together, produced roughly every ten minutes and limited to…
This definition is part of the Bitcoin Logical glossary. For the fuller explanation, start with Learn, or see the live numbers on The Bitcoin Signal.