Wei

Wei is the smallest denomination of ether, the native token of the Ethereum blockchain. One ether (1 ETH) equals 1,000,000,000,000,000,000 wei (10^18). Put differently, one wei is one quintillionth (10^-18) of an ether.

Key points

• A wei is to ether what a satoshi is to bitcoin: the atomic unit used for precise values and on-chain calculations.
• Ethereum gas (transaction fees) is quoted and paid in wei (commonly expressed as gwei).
• The unit is named after cryptographer Wei Dai, an early cypherpunk who proposed the b-money concept that influenced later cryptocurrency work.

How wei works

Digital currencies can be subdivided far more finely than fiat currencies. Ethereum uses wei as the base unit to avoid fractional rounding issues in smart contracts and protocol calculations.

To convert between ether and wei:
* ETH → wei: multiply by 10^18 (wei = ETH × 10^18)
* wei → ETH: divide by 10^18 (ETH = wei ÷ 10^18)

Example: 2.5 ETH = 2.5 × 10^18 = 2,500,000,000,000,000,000 wei.
Example: 1 wei = 10^-18 ETH.

Common ether subunits

Ethereum has several named subunits to make values easier to read and communicate:
* wei — 10^0 (base unit)
kwei (babbage) — 10^3 wei
mwei (lovelace) — 10^6 wei
gwei (shannon) — 10^9 wei (most commonly used for gas prices)
szabo — 10^12 wei
finney — 10^15 wei
ether — 10^18 wei

Gwei is the de facto unit for quoting gas prices because it balances granularity and readability.

Wei vs. gas

Wei is a monetary unit; gas is a measure of computational effort required to execute operations on Ethereum. Transaction fees are calculated as:

transaction fee (wei) = gas used × gas price (wei per gas)

Gas price is typically expressed in gwei, so users multiply the gas used by the gas price (in gwei) and then convert to wei/ETH as needed.

Who was Wei Dai?

Wei Dai is a computer engineer and cryptography enthusiast associated with the cypherpunk movement. He proposed the b-money concept in the 1990s, which outlined ideas about decentralized digital money and self-executing contractual enforcement. In recognition of his early influence on cryptocurrency and cryptography, Ethereum’s smallest unit was named “wei.”

Bottom line

Wei is the atomic unit of ether (1 ETH = 10^18 wei). Using such a small base unit ensures precision in transactions and smart contract calculations. For everyday interactions—especially gas pricing—gwei (10^9 wei) is the most commonly used denomination.