[Ethereum] the right way to calculate gas price and limit for contract deployment

contract-deploymentcontract-developmentmetamaskout-of-gasremix

I have tried several times and reached up to a gasPrice of 65 Gwei and a gasLimit of 500,000 which is $7.6 and still the deployment fails with error "Out of gas".

After spending tens of USD without getting the fees back – how can I calculate how much gas will be enough for deploying my contract?

Best Answer

If you are using Remix and MetaMask (ass your tags imply), then it should be calculated for you automatically (they use the eth_estimateGas RPC call under the hood). If that is the case, you should not manually enter a gasLimit of 500,000 and instead use their estimated gas.

As a note, any gas that is unused in the transaction is returned to you. For example, if your contract costs 1,000,000 gas to deploy and you use gasLimit = 5,000,000, then your contract will be deployed and you will only have spent 1,000,000 gas.

Related Solutions

[Ethereum] How Ethereum estimate the gas for running a contract

Geth does estimate the gas cost of a transaction, but theoretically no one--not geth, not the miners, nor anyone else--can know the gas cost of a transaction before it executed while creating a block. This is because something else could happen in a block before the transaction is executed (or even in the same block), thus changing the result that geth got when it made the estimate. It's even possible that geth made the estimate on a block that didn't even make it into the canonical blockchain.

Which brings the second point. geth gets its estimate by simulating the transaction itself, based on the latest block. There is essentially no other way to do so. This is called the Halting Problem, if you want to look it up, and it's why gas exists in the first place.

However, in most situations, sending the estimate is sufficient. It's even possible, in (IMHO) the majority of situations, to determine how much gas a transaction could ever possibly consume, and then use that.

Web3.js – How to Set Gas Price When Deploying a Contract?

From the documentation:

var contractInstance = MyContract.new([constructorParam1] [, constructorParam2],
  {data: '0x12345...', from: myAccount, gas: 1000000});

Yes, you can just add a gasPrice to that object:

var contractInstance = MyContract.new([constructorParam1] [, constructorParam2],
 {data: '0x12345...', from: myAccount, gas: 1000000, gasPrice: web3.toWei(2, 'gwei')});

Best Answer

Related Solutions

[Ethereum] How Ethereum estimate the gas for running a contract

Web3.js – How to Set Gas Price When Deploying a Contract?

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