Metamask: How to know the gas and gas limit when sending a transaction?

About Gas Limits and Sending Transactions on the Ethereum Network

As an Ethereum developer, it is essential to understand how gas limits work when sending transactions on the blockchain. In this article, we will dive deeper into the concept of gas limits, how to calculate them, and provide guidance on how to use them effectively.

What are gas limits?

Gas limits refer to the maximum amount of computing power (gas) that can be used by a transaction or smart contract execution. This limit is set by the Ethereum Virtual Machine (EVM) and ensures that transactions do not consume excessive resources, which can cause performance issues and potential errors.

Calculating Gas Costs

To calculate gas costs for a specific transaction, you will need to estimate the number of units of gas required. The EVM uses an algorithm called a “gas pricing schedule” to determine how much gas is needed for each block. This program takes into account factors such as network congestion, difficulty level, and block size.

The general formula for calculating gas costs is:

Gas Cost = (Block Size \* Gas ​​Price) / 1,000,000

Where Block Size is the number of bytes allocated to a transaction or contract execution and Gas Price is the current gas price per 1,000,000 units.

Here is an example calculation:

Let’s say you are running a smart contract that allocates 100 KB (102,400 bytes) for its body. The current gas price is $20 per 1,000,000 units.

Gas Cost = (100,000 bytes \* $20 per unit) / 1,000,000

Gas Cost ≈ 2,000 units of gas

About Gas Limits

When sending a transaction, you must consider the gas limit of both the sender’s account and the destination address. This ensures that the transaction does not exceed the available processing power.

To determine if the transaction is within the allowed gas limit:

• Calculate the total gas cost for the transaction using the gasPriceToGasCost function from the Web3 library (for example, w.eth.gasPriceToGasCost())

• Compare the calculated gas cost to the available processing power (represented by your account’s gas limit and the destination address)

• If the transaction is within the allowed gas limit, proceed with signing and transmitting.

Sample Code

Here is an updated sample code snippet that calculates gas costs for a smart contract method call:

const Web3 = require('web3');
const url = ' // Replace with your Infura project ID
const w = new Web3(url);
const accountAddress = 'YOUR_ACCOUNT_ADDRESS';
const targetAddress = 'TO_TARGET_ADDRESS';
// Calculate gas cost for transaction
async function calculateGasCost(transaction) {
const gasPriceToGasCost = await w.eth.gasPriceToGasCost();
const gasCost = (transaction.body.byteSize * gasPriceToGasCost) / 1,000,000;
return gasCost;
}
// Sign and broadcast the transaction using the calculated gas cost
async function sendTransaction(transaction) {
const gasCost = await calculateGasCost(transaction);
if (gasCost <= w.eth.gasLimit(accountAddress)) {
// Proceed with signing and broadcasting the transaction
} else {
throw new Error(Insufficient gas limit: ${gasCost} compared to available computing power: ${w.eth.gasLimit(accountAddress)});
}
}
// Example usage:
const smartContract = await w.ethereum.contracts.load('0x...'); // Replace with your contract address
const transaction = { method: 'someMethod', params: ['arg1', 'arg2'] };
sendTransaction(transaction);

Remember to replace the placeholders (e.g., YOUR_ACCOUNT_ADDRESS, TO_TARGET_ADDRESS, and 0x...) with your actual Infura project ID, account address, and contract address.

Best Practices

When sending transactions on Ethereum, follow these best practices:

• Always check if the transaction is within the allowed gas limit.

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