Wei

Wei is the smallest unit of ether (ETH), the native cryptocurrency of the Ethereum network. Just as a dollar can be divided into cents, one ETH can be divided into many smaller parts, specifically 1 ETH equals 1,000,000,000,000,000,000 wei (10^18). This extreme divisibility lets Ethereum represent tiny values precisely without relying on decimals.

On Ethereum, balances and transfers are ultimately accounted for in whole-number integers, and wei is the base unit that makes that possible. Wallets and interfaces may display ETH with decimals for readability, but under the hood, protocols and smart contracts typically use wei to avoid rounding errors. For example, a smart contract that distributes rewards or collects small payments can calculate exact amounts in wei, even when those amounts are far smaller than 1 ETH.

Wei is commonly encountered when discussing transaction fees, because gas prices are expressed in very small fractions of ETH. Many tools show gas prices in gwei, which equals 1,000,000,000 wei (10^9). Thinking in gwei makes fee settings easier for humans, while the network still settles everything in wei. When you send a transaction, the fee you pay is derived from gas used multiplied by a gas price, and the resulting amount is paid in wei.

Wei is also named after Wei Dai, a computer scientist known for ideas that influenced digital cash systems. Understanding wei matters because it underpins how Ethereum handles precision, smart contract accounting, and transaction fees across the entire ecosystem.