Glossary

Block Size

1 min read

The block size describes the amount of data which a block is allowed to take up, measured in bytes. Miners are not allowed to create a block with more data than the block size limit allows for, limiting the number of transactions miners can fit in each block.

This limit is in place to ensure the blockchain does not grow too rapidly in size, which would prevent average individuals from being able to maintain and query the blockchain. The block size limit is also the reason miners collect transaction fees based on the data size of the transaction. Miners are attempting to maximize the total fees they can collect per block.

Before SegWit activation, Bitcoin blocks were strictly limited to being at most 1MB. After SegWit, blocks are measured by weight rather than size. The maximum possible size of a block post-SegWit is now 4 MB.

Related Terms
SegWit
Segregated Witness (SegWit) is a soft-fork upgrade to Bitcoin which was activated in 2017. SegWit fixed the problem of transaction malleability, and paved the way for the implementation of the Lightning Network and many other upgrades.
Learn more.
Block Weight
Block weight is a measure of the size of a block, measured in weight units. The Bitcoin protocol limits blocks to 4 million weight units, equivalent to a maximum of 4 megabytes.
Learn more.
Mining
Mining is the process of building the blockchain by adding new blocks one at a time. Most of mining involves finding a valid Proof-of-Work, which is an energy-intensive guessing game.
Learn more.
Bitcoin Transaction Fee
All Bitcoin transactions must pay a fee to be included in the blockchain. The fee is paid to the miners. The higher the fee, the faster the transaction will be confirmed. Fees are measured based on the data size of the transaction.
Learn more.
vByte
A vByte is a unit of measure for the weight of blocks and transactions. A vByte is equivalent to 4 weight units, and thus, a block is limited to being 1 vMegabyte large, or 4 million weight units.
Learn more.
Explore More Terms →