Block Size

Block size is the amount of transaction data a bitcoin block can contain. Satoshi Nakamoto added a 1 megabyte limit in 2010 as an anti spam measure, and the 2017 segwit upgrade replaced it with a 4 million weight unit ceiling, which in practice allows blocks averaging around 1.5 to 2 megabytes, with a theoretical maximum near 4.

Why it matters

Block size sets the tradeoff between transaction throughput and decentralization. Bigger blocks fit more transactions and lower fees, but they make the blockchain grow faster and raise the cost of running a full node, concentrating validation among fewer operators. This tension produced the block size wars of 2015 to 2017, the most divisive conflict in Bitcoin's history, in which proposals to raise the limit were rejected and a faction split off in August 2017 to create Bitcoin Cash with larger blocks. The small block side won decisively: node accessibility was preserved and scaling effort moved to layers such as Lightning.

In the gold vs bitcoin debate

The block size saga is often cited as bitcoin's proof of hardness. Well funded companies and a majority of mining power backed bigger blocks, and the rule still did not change, because economic nodes refused. Gold's supply properties are protected by geology; the episode is the strongest evidence that bitcoin's properties are protected by a social consensus that has, so far, resisted concentrated pressure.