# Bitcoin blockspace basics

A short primer: blocks, weight, vbytes, fees, the mempool and the witness discount.

URL: https://blockspace.wiki/basics/

The on-ramp for newcomers and agents: what a block holds, how it is sized, and how its space is priced.

- [What is a block](https://blockspace.wiki/basics/what-is-a-block/): Blocks, transactions and the chain: what a Bitcoin block holds, how its size is counted, and how many there are.
- [Block weight and the limit](https://blockspace.wiki/basics/block-weight-and-the-limit/): Why a block's capacity is counted in weight units, the 4,000,000 WU consensus limit, and the 400,000 WU limit on a standard transaction.
- [Vbytes](https://blockspace.wiki/basics/vbytes/): The virtual byte: a quarter of a transaction's weight, the unit fee rates are quoted in, and why it differs from a transaction's raw size.
- [Fees and the mempool](https://blockspace.wiki/basics/fees-and-the-mempool/): Where a transaction waits before it is mined, how its fee is quoted in sat/vB, and what Blockspace Holdings' own node and fee estimates read.
- [The witness discount](https://blockspace.wiki/basics/the-witness-discount/): A witness byte weighs a quarter of a base byte, so it costs a quarter as much at the same fee rate. The short version, with links to the full page.
- [Halvings and the subsidy](https://blockspace.wiki/basics/halvings-and-the-subsidy/): The block subsidy, what Blockspace Holdings' documents say about it and the halving schedule, the fees beside it, and the sats coinbases never claimed.
- [Why blockspace is scarce](https://blockspace.wiki/basics/why-blockspace-is-scarce/): The fixed weight limit is the fact; what limits blockspace underneath it is Blockspace Value Theory's argument, labelled as theory.

Sources:

- Blockspace Value Theory · https://block.space/docs/bvt
- block.space docs: data types · https://block.space/docs/datatypes

Updated: 2026-10-20