Satoshi per byte (sat/byte or sat/vB) is the unit used to measure the fee rate of a Bitcoin transaction. It represents how many satoshis a user is willing to pay for every byte of data in their transaction. Miners use this metric to decide which transactions to include in the next block.
Definition
1 satoshi equals 0.00000001 BTC — the smallest indivisible unit of Bitcoin. When you send a transaction, you attach a fee. That fee divided by the size of your transaction in bytes gives you the sat/byte rate. The higher your rate, the more attractive your transaction is to miners.
Why Bytes Matter
Bitcoin's block size is capped at around 1 MB (or 4 million weight units). Miners can only fit a limited number of transactions per block, so they treat each block like a finite container. To maximize revenue, they fill it with transactions paying the highest sat/byte rates first.
Legacy vs SegWit
Before Segregated Witness (SegWit), fees were measured in satoshis per raw byte (sat/byte). After SegWit, the unit evolved to satoshis per virtual byte (sat/vB). Virtual bytes discount witness data by a factor of 4, keeping fees comparable between legacy and SegWit transactions.
Choosing Your Fee
During normal network conditions, 1–5 sat/vB is often enough for next-block confirmation. During congestion — such as market volatility or NFT/Ordinal inscription waves — rates can spike to 50–200+ sat/vB. Always check a mempool explorer before sending.
Understanding satoshi per byte (sat/vB) is the key to efficient Bitcoin transactions. Set your fee rate based on mempool conditions, use SegWit or Taproot addresses to reduce transaction size, and never pay more than the market demands.
Continue reading: Bitcoin Transaction Fee Calculator