Fee = vbytes × fee rate (sats/vB). Vbytes are virtual bytes — a SegWit-aware size that counts witness data at a 4× discount. Wallet-broadcast fee rate is set by the user; miners pick the highest-paying transactions first when assembling a block.
Satoshis per virtual byte — the unit Bitcoin fees are quoted in since SegWit. A 141 vB transaction at 5 sats/vB pays 705 sats total. The "vB" is unrelated to physical bytes on disk; it normalizes for the witness discount.
Witness-script data is discounted to 25% of its raw size when calculating vbytes. Taproot (and SegWit) put signatures and scripts in the witness, so a Taproot transaction is materially smaller in vbytes than a legacy P2PKH that puts everything into the input script.
Live from a public Bitcoin fee-estimation endpoint that aggregates current mempool conditions. The "fastest" tier estimates inclusion in the next block; lower tiers trade time for cost. The numbers update automatically every minute.
When the mempool is empty, even 1 sat/vB confirms quickly — that's the lowest tier the oracle reports. During congestion (NFT mints, surges, halving runs) fees can spike 100×. The economy tier waits for the next quiet stretch.