Gwei

Gwei is a unit of ether equal to one billion wei, or one-billionth of an ETH (0.000000001 ETH). The name is short for gigawei, and its main job is pricing gas: when Ethereum users and wallets talk about transaction fees, they quote the price per unit of gas in gwei because the numbers land in a convenient range — typically single digits to a few hundred, rather than unreadably long strings of zeros.

Every Ethereum transaction consumes gas, a measure of computational work, and the fee equals gas used multiplied by the gas price in gwei. For example, a simple ETH transfer uses 21,000 gas; at a gas price of 20 gwei, the fee is 420,000 gwei, which equals 0.00042 ETH. When the network is busy, users bid more gwei per gas to get included faster, so a "high gas" period simply means the going rate in gwei has risen.

A common misconception is that gwei measures the total cost of a transaction; it is only the price per unit of gas, so the actual fee also depends on how much gas the transaction consumes — a complex smart-contract interaction at 20 gwei costs far more than a simple transfer at 20 gwei. Since Ethereum's EIP-1559 upgrade, the gas price is split into a base fee that is burned and a priority tip to the validator, both still denominated in gwei.