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How Ethereum block sizes work

Created on August 2022 β€’ Tags: guidesethereum

An explainer showing how the block sizes work in Ethereum, and what is the maximum number of transactions in a block.

  • Ethereum has a limit in each block for amount of gas used.
  • Blocks are generated every 12 secs
  • Before the London Ethereum blockchain upgrade, there was a fixed size block. The London upgrade introcued variable size blocks.
  • There is a target of 15 million gas, but a maximum block size of 30 million (double the target block size).
  • If a block has more than 15 million gas then the base fee will increase for the next block, and if it is less than 15 million the fee will reduce for the next block. This is how it tries to keep the target always at 15,000,000.
  • There are four main things that contribute to gas usage in the EVM - memory usage, storage usage, transactional data, and what opcodes are run. See my guide on optimizing (reducing) gas usage in Solidity
  • Eth transfers cost 21k gas (so this means a theoretical limit of just over 1400 transfers). But smart contract calls can be much more expensive (100,000 gas usage isn’t uncommon, even a million+ is not rare)

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