Estimate Gas for Transaction

POST

https://eth-sepolia.nownodes.io/

Authorizations

ApiKeyAuthApiKeyAuth

api-key string

NOWNodes API key passed in the api-key header.

Changed. A call that sets blobVersionedHashes or authorizationList must include to. Without it the node rejects the request with an error (missing "to" in blob transaction or authorizationList provided for contract creation, but "to" field is missing). After the Amsterdam upgrade on Sepolia (October 6, 2026, 13:53:36 UTC) a plain value transfer is no longer estimated at a fixed 21000 gas: the node returns the gas the transfer actually uses under the new gas rules, so the result can differ from 0x5208.

Simulates a transaction and returns an estimate of how much gas would be used.

Body

application/json

Simulates a transaction and returns an estimate of how much gas would be used.

Request payload for Estimate Gas for Transaction.

jsonrpcstringrequired

JSON-RPC protocol version

methodstringrequired

The method name

paramsArray<object | string>required

The transaction call object and an optional block tag.

Show child attributes

Single JSON-RPC parameter value accepted by this method.

One of

fromstring

Address the transaction is sent from (optional)

tostringrequired

Destination address of the call

gasstring

Gas limit provided for execution (optional)

gasPricestring

Gas price in wei (optional)

valuestring

Amount of ETH to send, in hexadecimal wei (optional)

datastring

The compiled input data for the transaction (optional)

Optional block tag (e.g., "latest", "earliest", or a block number)

string

idintegerrequired

Request identifier

Response

200OK

Estimated gas amount

401Unauthorized

Unauthorized: API key is present but rejected by the NOWNodes gateway.

405Method Not Allowed

Method Not Allowed. Returned by the NOWNodes gateway for malformed or unsupported gateway-level requests.

422Unprocessable Entity

Missing API key. The NOWNodes gateway returns plain text for this error.

500Internal Server Error

Upstream node or gateway error.

Estimate Gas for Transaction

curl -X POST 'https://eth-sepolia.nownodes.io/' \
  -H 'Content-Type: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_estimateGas",
    "params": [
      {
        "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
        "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
        "gas": "0x76c0",
        "gasPrice": "0x9184e72a000",
        "value": "0x0",
        "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
      }
    ],
    "id": 1
  }'

import { JsonRpcProvider } from "ethers";

const provider = new JsonRpcProvider("https://eth-sepolia.nownodes.io/");
const result = await provider.send("eth_estimateGas", [
  {
    "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
    "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
    "gas": "0x76c0",
    "gasPrice": "0x9184e72a000",
    "value": "0x0",
    "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
  }
]);
console.log(result);

require 'eth'
require 'json'
require 'net/http'

uri = URI('https://eth-sepolia.nownodes.io/')
request = Net::HTTP::Post.new(uri)
request['Content-Type'] = 'application/json'
request.body = '{
  "jsonrpc": "2.0",
  "method": "eth_estimateGas",
  "params": [
    {
      "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
      "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
      "gas": "0x76c0",
      "gasPrice": "0x9184e72a000",
      "value": "0x0",
      "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
    }
  ],
  "id": 1
}'

response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
  http.request(request)
end

puts JSON.parse(response.body)

from web3 import Web3

w3 = Web3(Web3.HTTPProvider("https://eth-sepolia.nownodes.io/"))
response = w3.provider.make_request("eth_estimateGas", [
  {
    "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
    "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
    "gas": "0x76c0",
    "gasPrice": "0x9184e72a000",
    "value": "0x0",
    "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
  }
])
print(response)

import { createPublicClient, http } from "viem";

const client = createPublicClient({
  transport: http("https://eth-sepolia.nownodes.io/"),
});

const result = await client.request({
  method: "eth_estimateGas",
  params: [
  {
    "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
    "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
    "gas": "0x76c0",
    "gasPrice": "0x9184e72a000",
    "value": "0x0",
    "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
  }
],
});

console.log(result);

const endpoint = "https://eth-sepolia.nownodes.io/";
const apiKey = "YOUR_API_KEY";

async function nownodesRequest(payload) {
  const response = await fetch(endpoint, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "api-key": apiKey,
    },
    body: JSON.stringify(payload),
  });

  return response.json();
}

const result = await nownodesRequest({ jsonrpc: "2.0", method: "eth_estimateGas", params: [
  {
    "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
    "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
    "gas": "0x76c0",
    "gasPrice": "0x9184e72a000",
    "value": "0x0",
    "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
  }
], id: 1 });
console.log(result);

const response = await fetch('https://eth-sepolia.nownodes.io/', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
      "jsonrpc": "2.0",
      "method": "eth_estimateGas",
      "params": [
        {
          "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
          "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
          "gas": "0x76c0",
          "gasPrice": "0x9184e72a000",
          "value": "0x0",
          "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
        }
      ],
      "id": 1
    }),
});

const data = await response.json();

import requests

payload = {
  "jsonrpc": "2.0",
  "method": "eth_estimateGas",
  "params": [
    {
      "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
      "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
      "gas": "0x76c0",
      "gasPrice": "0x9184e72a000",
      "value": "0x0",
      "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
    }
  ],
  "id": 1
}

response = requests.post('https://eth-sepolia.nownodes.io/', json=payload)
data = response.json()

require 'net/http'
require 'json'

uri = URI('https://eth-sepolia.nownodes.io/')
request = Net::HTTP::Post.new(uri)
request['Content-Type'] = 'application/json'
request.body = '{
    "jsonrpc": "2.0",
    "method": "eth_estimateGas",
    "params": [
      {
        "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
        "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
        "gas": "0x76c0",
        "gasPrice": "0x9184e72a000",
        "value": "0x0",
        "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
      }
    ],
    "id": 1
  }'

response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |http| http.request(request) }
data = JSON.parse(response.body)

Request Body

{
  "jsonrpc": "2.0",
  "method": "eth_estimateGas",
  "params": [
    {
      "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
      "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
      "gas": "0x76c0",
      "gasPrice": "0x9184e72a000",
      "value": "0x0",
      "data": "0x70a08231000000000000000000000000a0df350d2637096571f7a701cbc1c5fd"
    }
  ],
  "id": 1
}

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x5208"
}

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32602,
    "message": "invalid argument 0: json: cannot unmarshal string into Go value of type ethapi.TransactionArgs"
  }
}

Unknown API_key

Method Not Allowed

Missing API_key

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32602,
    "message": "invalid argument 0: json: cannot unmarshal string into Go value of type ethapi.TransactionArgs"
  }
}