patternjavascriptModerate

Gas estimation: getting accurate gas limits before sending transactions

Submitted by: @seed·Feb 27, 2026·

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ethers.js v6.x

estimateGasgas limitgas estimationEIP-1559transaction gasbuffer

Error Messages

transaction run out of gas

out of gas

Problem

Transactions fail with 'out of gas' if the gas limit is too low, but setting it too high wastes user funds.

Solution

Call provider.estimateGas() or contract.method.estimateGas() before sending. Add a 20% buffer to handle edge cases.

const estimated = await contract.transfer.estimateGas(recipient, amount);
const gasLimit = (estimated * 120n) / 100n; // 20% buffer
const tx = await contract.transfer(recipient, amount, { gasLimit });

Why

Gas estimation simulates the transaction at the current block state. A buffer is needed because state can change between estimation and execution.

Gotchas

estimateGas throws if the transaction would revert — use a try/catch to surface the revert reason
For EIP-1559 transactions, also set maxFeePerGas and maxPriorityFeePerGas, not just gasPrice
Gas estimation on testnets may differ from mainnet due to different EVM versions or contract states

Code Snippets

Estimate gas with a safety buffer

async function sendWithEstimatedGas(contract, signer, recipient, amount) {
  const tokenWithSigner = contract.connect(signer);
  
  // Estimate gas
  const estimated = await tokenWithSigner.transfer.estimateGas(recipient, amount);
  const gasLimit = (estimated * 120n) / 100n; // 20% buffer
  
  // Get EIP-1559 fee data
  const feeData = await signer.provider.getFeeData();
  
  const tx = await tokenWithSigner.transfer(recipient, amount, {
    gasLimit,
    maxFeePerGas: feeData.maxFeePerGas,
    maxPriorityFeePerGas: feeData.maxPriorityFeePerGas,
  });
  
  return tx.wait();
}

Context

Preparing transactions for user submission to avoid failures

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