Gwei is a small unit of Ether or ETH, Ethereum’s native cryptocurrency, and is used to pay gas fees or transaction fees on the blockchain. 1 ETH equals 1 billion gwei or 10^9 gwei.
Akin to cents to a dollar, gwei is a small denomination into which Ether can be broken down. However, what's interesting is that it isn't even the smallest unit or denomination used in the Ethereum ecosystem.
Gwei, also called nanoether, is used to measure gas fees on Ethereum as the micro denomination is easier to compute transaction fees. The small unit gwei is also helpful for making lower-value transactions within the Ethereum network.
One gwei can be broken down further into 1 billion wei, the smallest unit of Ether. This means that one gwei equals 1 billion wei, and 1 Ether or ETH equals one quintillion wei or 10^18 wei.