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What does sats per vbyte mean?
Sats per vbyte (sat/vB) is the unit Bitcoin fees are quoted in: how many satoshis you pay for each virtual byte of block space your transaction takes. A satoshi is one hundred-millionth of a bitcoin. The fee depends on the transaction's size, not on the amount sent.
What it means for you
Your fee is the fee rate times your transaction's virtual size, so a payment that spends many small coins costs more than one spending a single large coin, even for the same amount. Too low a rate can leave a payment unconfirmed for a long time, and mixing up units is costly: sat/vB is 100,000 times smaller than BTC per kilo-vbyte.
A common mistake: “Sending more bitcoin costs a bigger fee.”
In fact: Bitcoin fees depend on the transaction's size in virtual bytes and the fee rate, not the amount. Sending a large amount from one coin can cost less than sending a small amount assembled from many coins.
How it works
SegWit (BIP-141) defines a transaction's weight as base size times 3 plus total size, and its virtual size as weight divided by 4, rounded up. Signature (witness) bytes therefore count a quarter as much as other bytes. The fee itself is whatever the inputs exceed the outputs by; fee levels move with demand for limited block space and with transaction size, not the amount transferred. Bitcoin Core accepts an explicit fee_rate in sat/vB and warns that a rate mistakenly given in BTC/kvB differs by a factor of 100,000.
An example
Say your transaction is 150 vbytes and your wallet suggests 10 sat/vB. The fee is 1,500 sats. If the same payment had to gather three small coins and grew to 300 vbytes, the fee at the same rate would be 3,000 sats.
Sources: BIP-141: Segregated Witness (transaction size calculations), Bitcoin Core 0.21.0 release notes (fee_rate in sat/vB), Bitcoin FAQ (bitcoin.org) · checked 4 October 2026
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