# 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.

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

A transaction has a size in bytes and a size in [vbytes](https://blockspace.wiki/glossary/vbytes/) (vB, virtual bytes). The second is the one fees are priced in. This page is the primer; the exact formulas are on [weight units and vbytes](/concepts/weight-units-and-vbytes/).

## The definition

block.space's data-types reference gives it:

```
vsize = ceil(weight / 4)
```

So a vbyte is a quarter of the [weight](https://blockspace.wiki/glossary/weight-unit/), rounded up for the transaction as a whole. Since a base byte weighs 4 WU and a [witness](https://blockspace.wiki/glossary/witness/) byte weighs 1 WU:

- a base byte counts as 1 vB;
- a witness byte counts as a quarter of a vB.

A transaction with no witness has the same size in bytes and in vbytes. A transaction that is mostly witness has about four times as many bytes as vbytes.

## Two real transactions

From the BTI case studies (2026-08-10):

| transaction | bytes | vbytes |
|---|---|---|
| the first BRC-20 mint, block 779,833 | 338 | 155 |
| a 3.9 MB jpeg inscription, block 960,962 | 3,911,459 | 977,936 |

The jpeg is almost all witness; the case study puts its ratio of bytes to vbytes, commit included, at about 4.00.

## Why the difference matters

Fee markets charge per vbyte (see [fees and the mempool](/basics/fees-and-the-mempool/)). The [raw bytes](https://blockspace.wiki/glossary/raw-bytes/) are, in the reference's words, "real bytes on disk and on the wire". [BTI](https://blockspace.wiki/glossary/bti/)'s design takes a side on which one measures blockspace: "raw bytes are the measure; vbytes are an observable." It keeps both on every row anyway, because the ratio between them shows how much of [the witness discount](/basics/the-witness-discount/) a protocol takes.

## The chain in both units

The census, as of block 972,315, 2026-10-20 11:58:41 UTC:

- raw bytes: 777.06 GB
- vbytes: 567.71 GB

block.space's boards offer a bytes and a vbytes toggle for the same reason.

Sources:

- block.space docs: data types · https://block.space/docs/datatypes
- Blockspace Holdings records
- block.space meter and summary APIs · https://block.space/api/summary
- block.space live pages (/, /rankings, /leaderboard, /largest-inscriptions, /heaviest-tokens, /collections, /sync) · https://block.space

Live figures: census as of block 972,315, 2026-10-20 11:58:41 UTC

Updated: 2026-10-20