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I am trying find the gas used by the transaction when a method is clicked in the remix solidity IDE. my code is as below. Value I am getting in the gasUsed variable is different to the value that is being shown on the etherscan explorer for this transaction. It would be helpful if someone helps me in correcting my code.

pragma solidity ^0.4.22;

contract id

uint public id;
uint public senderValue;
uint256 public gasUsed;

constructor() public 
 senderValue= msg.sender;


function setId(uint _id) public 
 uint256 gasInitial = gasleft();
 id= _id;
 setGasUsed(gasInitial - gasleft());


function setGasUsed(uint256 _gasUsed) private 
 gasUsed = _gasUsed;

The value of "gas used" in remix IDE is Execution Cost and the value of "Gas Used By Transaction" in etherscan is "Transaction cost".

Execution Costs are based on the cost of computational operations which are executed as a result of the transaction.

Transaction Costs are always based on the cost of which type of data you will send to blockchain. This depends on,

1. base cost of transaction (21000 gas)


2. the cost of a contract deployment (32000 gas)


3. the cost for every zero byte of data or code for a transaction.


4. the cost of every non-zero byte of data or code for a transaction.

You can understand easily by this image

Hope this answer clear your doubt.

Good question, I tested too. It means that, gasleft() equals 20020 gas before executing gasUsed2 = gasleft();. And after executing gasUsed2 = gasleft();, gasleft() = 0

test() transaction costs 61475 gas

gasUsed1 equals 40033 gas

gasUsed2 equals 20020 gas

pragma solidity ^0.4.22;

contract id 
 uint256 public gasUsed1;
 uint256 public gasUsed2;

 function test() public 
 gasUsed1 = gasleft();
 gasUsed2 = gasleft();