vByte

A vByte, or virtual byte, is bitcoin's post-SegWit unit of transaction size, defined so that 4 weight units equal 1 vByte, giving each block a capacity of 1 million vBytes. Fee rates are quoted in satoshis per vByte, and a typical single-input, two-output native SegWit payment comes to roughly 140 vBytes.

Why it matters

Block space is the scarce commodity of the bitcoin network, and the vByte is how it is metered. Miners rank waiting transactions by fee per vByte, so the number a wallet shows as sats per vByte is literally the bid being placed in the block space auction. Understanding it lets users time transactions to cheap periods, batch payments, and choose address types that consume fewer vBytes.

The unit also encodes a policy choice: witness data is discounted, making signature-heavy transactions cheaper per raw byte than data that lives in the UTXO set forever.

How it works

Transaction weight is computed as non-witness bytes times 4 plus witness bytes times 1, and vSize is that weight divided by 4, rounded up. A legacy transaction with no witness therefore has a vSize equal to its raw size, while SegWit transactions get an effective discount of up to 75 percent on their signature data.