Gas Cost & Estimation

Transaction Fee

Transaction fee = Gas units * Gas price

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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.

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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
}