Average Block Weight

What this measures

This chart tracks the average weight of mined blocks, in million weight units (MWU), based on mempool.space data. Since SegWit, weight is what defines a block’s capacity: a block cannot exceed 4 million weight units, or 4 MWU. The closer the average gets to that ceiling, the more of the available space is actually being used.

Weight, not size

Before SegWit activated in August 2017, the limit applied to the raw size of blocks: 1 megabyte. SegWit replaced it with a weight measure. Each byte of regular transaction data counts as 4 units, while each byte of witness data (the part that holds signatures, among other things) counts as just 1.

As a result, two blocks at 4 MWU do not necessarily contain the same number of bytes. A block made up only of legacy transactions tops out at 1 MB, while a block rich in witness data can go well beyond that. The vbyte, used for fees, is simply weight divided by 4: 4 MWU equals 1 million vbytes.

A full block is not always at 4 MWU

An average slightly below the ceiling does not mean there was room to spare. Miners keep a small margin for their own transaction, the one that pays out the reward (the coinbase), and assembling a block sometimes leaves small gaps that nothing in the queue can fill. Empty blocks, which some pools mine right after a new block is found, also drag the average down. Demand pressure is better read in mempool size.

A limit defended, not overlooked

This ceiling is a deliberate compromise. Between 2015 and 2017, the block size debate pitted those who wanted to raise the chain’s capacity against those who saw keeping a full node within reach of individuals as the priority. It ended in 2017 with SegWit’s activation on one side, and the Bitcoin Cash split, which opted for bigger blocks, on the other.

The discount granted to witness data had a side effect. Since 2023, Ordinals inscriptions have been storing images and other files there at a reduced price, producing the largest blocks in bytes in the network’s history.

🪙 What are Ordinals, Runes, and other inscriptions on Bitcoin?

Some see it as a legitimate use of space paid for at market price. Others see it as an abuse that bloats the chain every node has to store. The protocol itself makes no distinction.

Full blocks prove there is demand for block space. They do not prove that space is being used for payments.