The unit of fee for transactions on Ethereum is called "gas," which measures the amount of computational effort required for operations on the network. Gas fees are paid in a denomination of Ether called "gwei," where 1 gwei equals 10−910^{-9}10−9 ETH. For example, a simple transaction like sending ETH consumes 21,000 units of gas, and the fee is calculated as gas units multiplied by the gas price in gwei (tip plus base fee).