What is a Wei?

Wei is the smallest denomination of ether, the cryptocurrency coin used on the Ethereum network.

1 ether = 1,000,000,000,000,000,000 wei (1018). The other way to look at it is one wei is one quintillionth of an ether.

Key Takeaways

  • A wei is to ethereum as a satoshi is to bitcoin: both units are the smallest unit from which a user may make a transaction.
  • A U.S. dollar is only divisible into 100 unitspenniesand the penny is the indivisible (atomic) unit of U.S. currency.
  • The wei is named after Wei Dai, best known as the creator of the bitcoin predecessor "b-money" and as the developer of the Crypto++ library.

How a Wei Works

As the price of cryptocurrencies grew at though 2017, people not in the crypto world wondered how you make change out of a $17,000 bitcoin. A U.S. dollar is only divisible into 100 parts, and a penny is the atomic unit of U.S. currency. But digital cryptocurrencies are divisible into much, much smaller units.

To correctly denote the quantity of a transaction that may appear to be a very small fraction in terms of ether but a high value when converted to U.S. dollars or other real-world currencies, new units have been named to correctly identify and support the transactions. The smallest unit of the ethereum cryptocurrency is called the wei after Wei Dai, a cryptography activist who is known for supporting the widespread use of strong cryptography and privacy-oriented technologies.

Unlike other cryptocurrencies (bitcoin, for example, only has the satoshi as a common sub-unit), ether has many names for different numbers of wei. The names of these sub-units indicate the quantity of the units (for example, a kwei is a kilo, meaning a thousand wei), but they have informal names as well. The kwei is also known as an "ada" and a gwei is also called a "shannon."

Sub-units of Ethereum
Unit wei value wei ether value
wei 1 wei 1 10^-18 ETH
kwei 10^3 wei 1,000 10^-15 ETH
mwei 10^6 wei 1,000,000 10^-12 ETH
gwei 10^9 wei 1,000,000,000 10^-9 ETH
microether 10^12 wei 1,000,000,000,000 10^-6 ETH
milliether 10^15 wei 1,000,000,000,000,000 10^-3 ETH
ether 10^18 wei 1,000,000,000,000,000,000 1 ETH


The Wei's Real-Life Exemplar

Wei Dai has been called an "intensely private" person, and with his skills in cryptography, he's able to make sure the public record of him is very small. We do know that he graduated from the University of Washington with a degree in Computer Science and that he worked at Microsoft in its cryptography research group.

According to VoteHere.net as cited here, "Mr. Dai worked in the Cryptography Research Group at Microsoft Corporation in Redmond, Washington. While at Microsoft, he was involved in the study, design and implementation of cryptosystems for specialized applications. Prior to joining Microsoft, Mr. Dai was a programmer with TerraSciences of Acton, Massachusetts."

Wei is an original member of the cypherpunk movement in the 1990s whose members eventually developed the theoretical basis for cryptocurrency in the 2010s. In his proto-crypto manifesto for a cryptocurrency called bmoney, Wei laid the foundation for "smart contracts" that would self-execute and not need intervention by a human third party for enforcement. For this innovation, he is honored by having the name of the atomic unit of ether named after him.