{"id":18504,"date":"2020-08-17T04:00:00","date_gmt":"2020-08-17T04:00:00","guid":{"rendered":"http:\/\/ci027d03ed20192697"},"modified":"2025-10-02T15:07:25","modified_gmt":"2025-10-02T20:07:25","slug":"what-is-the-bitcoin-block-size-limit","status":"publish","type":"post","link":"https:\/\/bitcoinmagazine.com\/guides\/what-is-the-bitcoin-block-size-limit","title":{"rendered":"What Is The Bitcoin Block Size Limit?"},"content":{"rendered":"
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The Bitcoin block size limit is a parameter in the Bitcoin protocol that limits the size of Bitcoin blocks, and, therefore, the number of transactions that can be confirmed on the network approximately every 10 minutes. Although Bitcoin launched without this parameter, Satoshi Nakamoto added a 1 megabyte block size limit back when he was still the lead developer of the project. This translated into about three to seven transactions per second, depending on the size of transactions.<\/p>\n

Further Reading: Who Created Bitcoin?<\/a><\/em><\/strong><\/p>\n

In 2017, Bitcoin\u2019s block size limit was replaced by a block weight<\/em> limit of 4 million \u201cweight units.\u201d This changed how data in blocks is \u201ccounted\u201d: some data weighs more than other data. Perhaps more importantly, it also represented an effective block size limit increase: Bitcoin blocks now have a theoretical maximum size of 4 megabytes and a more realistic maximum size of 2 megabytes. The exact size depends on the types of transactions included.<\/p>\n

Why Is the Block Size Limit Controversial?<\/h2>\n

The block size limit is controversial because there is disagreement over whether or not such a limit \u201cshould be\u201d part of the Bitcoin protocol, and if it should, how big it should be.<\/p>\n

Satoshi Nakamoto never publicly specified why he added a block size limit to the Bitcoin protocol. It has been speculated that he intended it to be an anti-spam measure, to prevent an attacker from overloading the Bitcoin network with artificially large Bitcoin blocks full of bogus transactions. Some have also been speculated that he intended for it to be a temporary measure, but it is unclear how temporary or under what conditions he foresaw the block size limit being increased or lifted. The code itself that enforces the block size limit certainly wasn\u2019t temporary.<\/p>\n

Further Reading: Can Bitcoin Scale?<\/a><\/em><\/strong><\/p>\n

A couple years after Satoshi Nakamoto left the project, developers and users started to disagree on the temporality and necessity of the block size limit. As Bitcoin\u2019s user base grew, some believed it was time to increase or lift the block size limit entirely, specifically before Bitcoin blocks would start filling up with transactions. Others came to believe that the block size limit represents a vital security parameter of the protocol and believed it should not be lifted \u2014 or at least, it should be lifted more conservatively. Yet others think that the 1 megabyte put in place by Satoshi Nakamoto was actually too<\/em> large and advocated for a block size limit decrease<\/p>\n

.Adding more complications, since Bitcoin is decentralized, no particular group or person is in charge of decisions like increasing or decreasing the block size. Disagreements on how such decisions should be made, by whom, or if they should be made at all, has probably led to at least as much controversy as the block size limit itself \u2014 but this aspect of the debate is outside the scope of this article.<\/p>\n

Further Reading: What Is Bitcoin?<\/a><\/em><\/strong><\/p>\n

Why Shouldn\u2019t Bitcoin Blocks Be Too Small?<\/h2>\n

Note: Almost anything about Bitcoin\u2019s block size limit and the risks of it being too big or too small is contested, but these are some of the more general arguments.<\/em><\/p>\n

If Bitcoin blocks are too small, not many transactions can be processed by the Bitcoin network. Broadly speaking, proponents of a block size limit increase (\u201cbig blockers\u201d) argue this can have two negative consequences.<\/p>\n

Not Enough Space?<\/h2>\n

Firstly, smaller bitcoin blocks would mean that there isn\u2019t enough space to include everyone\u2019s transactions in these blocks, and the transaction fee \u201cbidding war\u201d to get transactions confirmed would price most people out of using bitcoin at all. Instead, it could lead to a future where only bank-like institutions make transactions with one another, while regular users hold accounts with these institutions. This would, in turn, open the door to fractional reserve banking, transaction censorship and more of the problems with traditional finance that many bitcoiners hoped to get away from.<\/p>\n

Deterrent to Adoption<\/h2>\n

Secondly \u2014 and this is probably what many \u201cbig blockers\u201d consider to be a more pressing concern \u2014 users would simply give up on Bitcoin altogether because blocks are too small. Perhaps users would switch to a competing cryptocurrency or they would give up on this type of technology altogether.<\/p>\n

Why Shouldn\u2019t Bitcoin Blocks Be Too Big?<\/h2>\n

Note: Almost anything about Bitcoin\u2019s block size limit and the risks of it being too big or too small is contested, but these are some of the more general arguments.<\/em><\/p>\n

Opponents of a block size limit increase (\u201csmall blockers\u201d) argue there are, roughly speaking, three risks if blocks are too big, each of which have several \u201csub-risks\u201d as well as nuances.<\/p>\n

Increased Cost for Bitcoin Nodes<\/h2>\n

The first of these risks is that bigger blocks increase the cost of operating a Bitcoin node. It increases this cost in four ways:<\/p>\n