Gas Cost Estimation – How to Estimate Gas Cost for Contract Method Using Geth

The documentation is skimpy on details and it took me forever to figure out the correct way with the help of your links, anyways, here is what works for me:

Tested on Geth : 1.6.7 -stable , web3.js :0.20.2 Parity/v1.7.2 & Kovan testnet.

I'll be using the minimal token as example :

pragma solidity ^0.4.0;

contract minimalToken {

     mapping (address => uint256) public balanceOf;

    function minimalToken(uint256 initialSupply) {
        balanceOf[msg.sender] = initialSupply;
    }

    function transfer(address _to, uint256 _value) {
        require(balanceOf[msg.sender] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;
    }
}

I'll be focusing on the transfer method which takes 2 arguments,( address, amount) to transfer:

    var contract = web3.eth.contract(contractABI).at("0x8caaa1f263ff14d0276ff1a1a6ed15c51159d6e0");
    var receiverAddress = '0x00Ce6C92856A657979E7728005DBc9acD002Eb09';
    var callData = contract.transfer.getData(receiverAddress, 2000);

    var gasEstimate = web3.eth.estimateGas({
        from: web3.eth.coinbase,
        to: "0x8caaa1f263ff14d0276ff1a1a6ed15c51159d6e0",
        data: callData
    });

    var gasPrice = web3.eth.gasPrice;

    console.log('gas Price: ' + gasPrice);
    console.log('Estimated Transaction gas: ' + gasEstimate);

// gas Price: 21000000000
// Estimated Transaction gas: 34207

One thing that Threw me off, was that I kept on getting transaction errors due to me not including the from: field on the transaction.

Hope this helps.

Try using .getData().

.getData() returns the encoded parameters of a function in order to send the transaction manually. You can then stick this in web3.eth.estimateGas() (the one on web3.eth, not on a given method.) to simulate sending the transaction.

Here's an untested example, but hopefully it can help you on your way:

var contractData = contractObject.new.getData(someparam, another, {data: contractBytecode});
var estimate = web3.eth.estimateGas({data: contractData})

References:

web3.eth.estimateGas()

An example of using .getData() (It's the fourth option.)