Estimate gas price with ethers.js

Question

I'm looking to estimate transaction fees in an application. In order to do so I need to estimate the current gas price before I execute the transaction.

I see web3.js has a getGasPrice method: https://web3js.readthedocs.io/en/v1.3.4/web3-eth.html#getgasprice

Is there a similar method in ethers.js? Or what is the recommended approach here?

Answer 1

There is a method called estimateGas in the Contract class. Example for how to use it:

const erc20Abi = [ /* ... */ ];
const address = "TOKEN_ADDRESS_HERE";
const provider = ethers.getDefaultProvider();
const erc20 = new ethers.Contract(address, abi, provider);

const recipient = "SOME_ADDRESS_HERE";
const estimation = await erc20.estimateGas.transfer(recipient, 100);

Caveats:

1. You have to be connected to a provider, but luckily this is easy to do with the getDefaultProvider function.
2. Don't expect the gas estimation to be super precise, especially when your contract call is making additional calls to other contracts.

Answer 2

Found it! https://docs.ethers.io/v5/api/providers/provider/#Provider-getGasPrice

Hint: the search functionality on docs.ethers.io isn't great - this method didn't show up by searching for "gasprice": https://docs.ethers.io/v5/search/?search=gasprice

Answer 3

As of 2022 you should use getFeeData() since getGasPrice() has been deprecated. This accounts for network fee changes introduced in EIP-1559. The creator of Ethers.js talks about this in the above link and also provided an example of how to use it.

getGasPrice() documentation: https://docs.ethers.io/v5/api/providers/provider/#Provider-getFeeData