Wei to ETH Converter

Ethereum units explained

Ether is divisible down to the wei, the smallest unit. Every denomination is just a power of ten of wei, so converting is a matter of shifting the decimal point. Nothing on chain is ever stored as a fraction: the EVM only knows integers, and "1.5 ETH" is really 1500000000000000000 wei with a decimal point drawn in by your wallet.

Converting in ethers.js, viem and web3.js

Do not write the multiplication yourself. Every library ships a parse and a format function that take a decimal string and return a bigint, or the other way round, and they handle the awkward cases you will otherwise rediscover one at a time. On BLAZED.sh, ethers.js and web3.js are pre-installed in the script editor, so these run with no setup.

// ethers.js v6
import { parseEther, formatEther, parseUnits, formatUnits } from "ethers";

parseEther("1.5");              // 1500000000000000000n
formatEther(1500000000000000000n); // "1.5"

parseUnits("20", "gwei");       // 20000000000n  (a gas price)
formatUnits(20000000000n, "gwei"); // "20.0"

// ERC-20: always read decimals(), never assume 18
const decimals = await token.decimals();      // 6 for USDC
parseUnits("25.50", decimals);                // 25500000n

// viem
import { parseEther, formatEther, parseGwei } from "viem";
parseEther("1.5");   // 1500000000000000000n
parseGwei("20");     // 20000000000n

// web3.js v4
import { utils } from "web3";
utils.toWei("1.5", "ether");        // "1500000000000000000"
utils.fromWei("1500000000000000000", "ether"); // "1.5"

# Python, web3.py
from web3 import Web3
W3 = Web3()
W3.to_wei("1.5", "ether")   # 1500000000000000000
W3.from_wei(20000000000, "gwei")  # Decimal('20')

Three ways the conversion goes wrong

The first is floating point. A JavaScript number carries roughly 15 significant digits and an ether amount needs 18, so the moment a wei value passes through a Number() or a JSON.parse of an unquoted number, the tail is gone. It will look right in testing, because small round amounts survive, and it will be wrong on the first real balance.

The second is token decimals. Wei is a property of ether, not of every token. USDC has six decimals, so 25.50 USDC is 25500000, and code that reuses parseEther for it will try to move a trillion times too much and revert, or worse, succeed in the other direction. Read decimals() once per token and cache it.

The third is the wire format. JSON-RPC returns quantities as minimal hex strings, so a balance comes back as "0x14d1120d7b160000" and not as a decimal. BigInt(hex) is the safe conversion; the hex to decimal converter does the same thing by hand when you are debugging a raw response, and the eth_getBalance reference shows the exact shape of the reply.

Frequently asked questions