sat/vB (satoshis per virtual byte)

A Bitcoin transaction’s fee depends on its size, not on the amount sent: size in vbytes × rate in sat/vB = fee in satoshisGlossarySatoshi (sats)The smallest unit of Bitcoin: 1 satoshi (‘sat’ for short) equals 0.00000001 BTC, so one bitcoin consists of 100 million sats. The unit is named after Bitcoin’s creator, Satoshi Nakamoto.On the learning path: Stage 1 · Step 4 – Sats & units →In the glossary →×.

What is a virtual byte?

Since SegWitGlossarySegWit (Segregated Witness)A 2017 soft fork that treats signature data (the ‘witness’) separately. It fixed transaction malleability, increased block capacity and makes payments with modern addresses (bc1q…) cheaper.In the glossary →×, signature data (the ‘witness’) counts for only a quarter of a transaction’s weight. The size in vbytes is the weight divided by four; a block holds at most 4 million weight units.^[1] That’s why sending from modern addresses (bc1q…, bc1p…) is usually cheaper than from old ones starting with 1.

Worked example

A simple payment from a bc1q address (one input, two outputs: recipient and change) is around 141 vbytes.^[2] At 5 sat/vB it costs 141 × 5 = 705 sats; at 20 sat/vB, 2,820 sats. At an example price of $80,000 per BTC, that’s around $0.56 or $2.26 (own calculation).

What rate you need right now

That depends on how full the mempoolGlossaryMempoolThe buffer in which a node collects valid but still unconfirmed transactions until a miner includes them in a block. There is no central mempool – every node keeps its own.On the learning path: Stage 5 · Step 4 – First withdrawal →In the glossary →× is. Right now, about 2 sat/vB is enough for the next block, and about 1 sat/vB for confirmation within roughly an hour. Wallets convert tiers such as ‘slow’ or ‘fast’ into sat/vB for you.

Since version 29.1 (September 2025), Bitcoin Core relays transactions from 0.1 sat/vB by default; before that, only from 1 sat/vB.^[3],[4] Whether miners include such cheap transactions promptly depends on demand. If a payment gets stuck, you can often raise the fee with replace-by-feeGlossaryReplace-by-fee (RBF)A method of replacing a still-unconfirmed transaction with a new version that pays a higher fee. This lets you speed up a stuck payment, as long as it isn’t in a block yet.On the learning path: Stage 5 · Step 4 – First withdrawal →In the glossary →×. More under Bitcoin transactions & fees.