Gas Cost & Estimation

Transaction Fee

Transaction fee = Gas units * Gas price

Core Concepts

• 
  Gas units: unit of computation for executing an operation.
  


• 
  Gas price: how much ETH you pay for every gas unit, it is composed of base fee and priority fee (tip).
  


• 
  Gas limit: the maximum gas you allow for one transaction.

Important Mechanism

• 
  Gas refund: unused gas will be refunded to sender after the transaction finish.
  


• 
  Out of Gas: if gasUsed > gasLimit, transaction will fail and rollback all state changes, but the gas already used will not be refunded.
  


• 
  Batching: better to split heavy computation into multiple smaller transactions to avoid exceeding gas limit.
  

// ❌ Bad:

// function doMassiveLoop() public {

//     for (uint i = 0; i < 1000000; i++) {

//         // ... do work

//     }

// }



// ✅ Good: batches

uint public start = 0;

uint public constant INCREMENT = 100;



function doWorkInBatches() public {

    uint end = start + INCREMENT;

    for (uint i = start; i < end; i++) {

        // ... only do small part of work

    }

    start = end; // update next starting index

}