How to calculate "gas" and "gasPrice" when referring to ethgasstation.info when sending transaction via web3js?

Question

I'm using web3js to issue token which has a name and description. I'm using ropsten testnet.

Here's my tx.

const tx = {
      from: walletAddress,
      to: contractAddress,
      gas: 4700000,
      gasPrice: 20000000000,
      data: encodedABI,
    };

Here's what ethgasstation.info is telling me now.

I'm confused about how to translate what I read on ethgasstation.info to my "gas" and "gasPrice" values. I kept getting "ran out of gas" error if I only set gas to 2000000 WITHOUT specifying gasPrice.

Answer 1

The value for gas depends on the type of transaction that you want to execute.

If it's a transfer of ether into an externally-owned account, then you can simply set it to 21000.

If it's a smart contract function, then it depends on the actual function. If you have 100% confidence in the function (e.g., it is your function and you know that it's not going to drain out "tons of gas"), then you can simply use a very large value (though not larger than the current block limit, which unfortunately is not specified on ethgasstation.info).

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The value for gasPrice should be what you want, and the tradeoff is "higher price ==> faster execution, lower price ==> slower execution".

ethgasstation.info tells you the average or median (not really sure) price of the last N (not really sure) blocks.

In your screenshot, it tells you that this price is 5gwei, which translates to "5" followed by 9 zeros.

It also tells you that if you use this price, then the expected time for the execution of your transaction is 0.4 minutes.

If you don't specify a value for gasPrice, then the node executing your transaction will use the current price on the network.