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Estimating Transaction Fees
A tutorial showing how to accurately estimate the total transaction fees for a transaction on Mantle Network
In this tutorial, we'll be looking at an example that shows how to use the Mantle SDK to estimate the total gas fees for a transaction on Mantle Network, which is a combination of the layer-2 (L2) execution fee, and the layer-1 (L1) rollup fee.
In SDK version
@mantleio/sdk @0.2.2 , we're introducing the parameters required to make accurate estimations of the L1 rollup fee that will be incurred for sending a transaction at any given time. The calculation to obtain L1 rollup fee is as follows:L1RollupFee = L1GasPrice * Overhead * Scalar * Ratio
There are 4 interfaces available as part of the SDK, where:
L1GasPrice * Ratiocan be fetched by calling thegetL1GasPricemethod. It invokes thel1basefee()function of theBVM_GasPriceOraclecontract.overhead,decimals, andscalarvalues can be fetched from theBVM_GasPriceOraclecontract by calling the respective SDK methods with the same names.
The
decimals value in the contract is mainly used to control the precision of scalar, which helps ensure accurate L1 rollup fee calculation.The L2 execution fee, on the other hand, is calculated as follows:
L2TxnFee = L2GasPrice * L2GasUsed
- L2 gas price is fetched by calling the
getGasPricemethod - The gas used to execute a transaction is fetched by calling the
estimateGasmethod
The total gas fee is thus calculated as:
totalEstimatedGasFee = L1RollupFee + L2TxnFee
Before proceeding, please make sure you have
npm installed and configured in your local environment.Start by installing Mantle SDK and the necessary dependencies in your environment by running the following command:
npm install @mantleio/sdk
If you already have the SDK installed, please make sure you update to the latest version by running the command
npm update @mantleio/sdk since the L1 rollup fee parameters are only available for version 0.2.2, or higher.You can directly use the following JS code to estimate the total gas fees.
const ethers = require("ethers")
const mantleSDK = require("@mantleio/sdk");
async function estimateGasFee() {
const l2RpcProvider = new ethers.providers.JsonRpcProvider("https://rpc.mantle.xyz")
try{
// Arbitrary tx object
const tx = {
to: '0x...',
value: ethers.utils.parseEther("0.1"), // Returns value in wei
};
// By calling the BVM_GasPriceOracle contract method l1basefee()
const gasPrice = await mantleSDK.getL1GasPrice(l2RpcProvider);
const decimals = await mantleSDK.decimals(l2RpcProvider);
const scalar = await mantleSDK.scalar(l2RpcProvider);
const gasUsed = await mantleSDK.overhead(l2RpcProvider);
// L1RollupFee
const l1RollupFee = gasPrice.mul(gasUsed).mul(scalar).div(10**decimals)
// L2TxnFee
const l2Gas = await l2RpcProvider.estimateGas(tx)
const l2GasPrice = await l2RpcProvider.getGasPrice()
const l2TxnFee = l2GasPrice.mul(l2Gas);
// Total estimated Gas Fee
const totalEstimatedGasFee = l1RollupFee.add(l2TxnFee);
console.log(`Total estimated Gas Fee: ${totalEstimatedGasFee.toString()}`);
} catch (error) {
console.error('Error estimating gas:', error);
}
}
estimateGasFee();
totalEstimatedGasFee contains the final result of the calculation, as discussed in the Description section.Last modified 2mo ago