Library · Crypto, word by word · Inside Ethereum
What is wei?
Wei is the smallest unit of ether: one ETH equals 10^18 wei, a 1 followed by 18 zeros. Gwei, equal to 10^9 wei, is the unit usually used for gas prices.
What it means for you
Transactions and contracts record amounts in wei, so raw data on a block explorer or in a signing request can show a huge integer for a small amount. Miscounting the 18 decimal places misreads an amount by factors of a thousand or more; the converted ETH figure is the one to check before confirming.
How it works
At the protocol level every amount of ether is a whole number of wei. Each transaction's value field gives the ether to send in wei, and each account's balance field is the number of wei it owns, so software performs its calculations in wei and converts for display. The common named units are wei, gwei (10^9 wei, or 10^-9 ETH) and ether (10^18 wei).
An example
Say a transaction's value field reads 50000000000000000. That is 5 x 10^16 wei, which is 0.05 ETH. A gas price of 20 gwei is 20,000,000,000 wei per unit of gas.
Sources: ethereum.org: Intro to ether, ethereum.org glossary, ethereum.org: Ethereum accounts · checked 4 October 2026
Related words
Educational content, not financial advice. Written by hand and checked against the source named above. Something wrong? Tell us and we reply within two business days.