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A Summary of

Accounts, transactions, gas, and block gas limits in Ethereum

Hudson Jameson
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Understand some of the basic mechanics behind accounts, transactions, gas, and the role miners play in setting the block size in Ethereum. 

An externally controlled account

  • Has an ether balance, can send transactions (ether transfer or trigger contract code), is controlled by private keys, has no associated code.

Contract accounts

  • Every time a contract account receives a transaction, its code is executed as instructed by the input parameters sent as part of the transaction. 


  • The term “transaction” refers to the signed data package that stores a message to be sent from an externally owned account to another account on the blockchain.


  • Contracts have the ability to send “messages” to other contracts. Messages are virtual objects that are never serialized and exist only in the Ethereum execution environment.

What is gas?

  • For every executed operation there is a specified cost, expressed in a number of gas units.

Gas and transaction costs

  • Every transaction is required to include a gas limit (sometimes called StartGas) and a fee per gas.

Estimating transaction costs

  • Total cost = gasUsed * gasPrice


  • gasUsed is the sum of all the gas for all the operations executed.

What is “block gas limit”?

  • Block gas limits are the maximum amount of gas allowed in a block to determine how many transactions can fit into a block. 

What is a “DoS” of the Ethereum network?

  • Recently there have been reports of the Ethereum network slowing down or becoming unusable.
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