---
title: "What is Ethereum mainnet chain ID?"
url: "https://worldwiki.io/q/what-is-ethereum-mainnet-chain-id"
type: "question"
language: "en"
intent: "informational"
entity: "Blockchain Mainnet"
topic: "Blockchain"
published: "2026-09-18 07:10:23"
updated: "2026-09-18 16:10:23"
---

# What is Ethereum mainnet chain ID?

## Short answer

Ethereum mainnet uses chain ID 1. Chain IDs were introduced by EIP-155, created on 14 October 2016. The proposal builds a chain identifier into transaction signatures, so a transaction signed for one network cannot be replayed on another, such as Ethereum Classic or a testnet. Older Ethereum testnets had their own IDs, for example 3 for Ropsten and 5 for Goerli.

## Answer

EIP-155 also lists 1337 as the default chain ID for Geth private chains [10]. Checking the chain ID in a wallet or tool is a practical way to confirm you are on mainnet.

## Related questions

- [What is a blockchain mainnet?](https://worldwiki.io/q/what-is-a-blockchain-mainnet)
- [Are testnet tokens worth real money?](https://worldwiki.io/q/are-testnet-tokens-worth-real-money)
- [What does mainnet launch mean in crypto?](https://worldwiki.io/q/what-does-mainnet-launch-mean-in-crypto)
- [How are blockchain mainnet upgrades done?](https://worldwiki.io/q/how-are-blockchain-mainnet-upgrades-done)
- [What is the difference between mainnet and testnet?](https://worldwiki.io/q/what-is-the-difference-between-mainnet-and-testnet)

## Sources

1. [Blockchain Technology Overview (NISTIR 8202)](https://arxiv.org/abs/1906.11078) — National Institute of Standards and Technology (via arXiv) · evidence page: https://worldwiki.io/source/171
2. [Networks](https://ethereum.org/developers/docs/networks/) — ethereum.org · evidence page: https://worldwiki.io/source/172
3. [Holesky and Hoodi Testnet Updates](https://blog.ethereum.org/2025/03/18/hoodi-holesky) — Ethereum Foundation Blog · evidence page: https://worldwiki.io/source/173
4. [Pectra Mainnet Announcement](https://blog.ethereum.org/2025/04/23/pectra-mainnet) — Ethereum Foundation Blog · evidence page: https://worldwiki.io/source/174
5. [Holešky Testnet Shutdown Announcement](https://blog.ethereum.org/2025/09/01/holesky-shutdown-announcement) — Ethereum Foundation Blog · evidence page: https://worldwiki.io/source/175
6. [Solana Clusters](https://solana.com/docs/references/clusters) — Solana Foundation · evidence page: https://worldwiki.io/source/176
7. [Using a test network](https://bitcoincore.academy/testnets.html) — Bitcoin Core Onboarding · evidence page: https://worldwiki.io/source/177
8. [Genesis block](https://en.bitcoin.it/wiki/Genesis_block) — Bitcoin Wiki · evidence page: https://worldwiki.io/source/178
9. [Ethereum Launches Long-Awaited Decentralized App Network](https://www.coindesk.com/markets/2015/07/30/ethereum-launches-long-awaited-decentralized-app-network) — CoinDesk · evidence page: https://worldwiki.io/source/179
10. [EIP-155: Simple replay attack protection](https://eips.ethereum.org/EIPS/eip-155) — Ethereum Improvement Proposals · evidence page: https://worldwiki.io/source/180
11. [The Merge](https://ethereum.org/roadmap/merge/) — ethereum.org · evidence page: https://worldwiki.io/source/160
12. [Taproot](https://bitcoinops.org/en/topics/taproot/) — Bitcoin Optech · evidence page: https://worldwiki.io/source/181