Gwei is a denomination of Ether (ETH) commonly used to express gas prices on the Ethereum network. One gwei equals 0.000000001 ETH (10⁻⁹ ETH), or one billionth of an Ether.
Why Gwei Exists
Gas fees on Ethereum are typically tiny fractions of an ETH. Instead of saying a transaction costs 0.000000020 ETH, it's much clearer to say it costs 20 gwei. The unit makes gas pricing human-readable.
Ether Denominations
Wei: The smallest unit (1 ETH = 10¹⁸ Wei).
Gwei (Gigawei): 1 billion Wei (1 ETH = 10⁹ Gwei). Used for gas prices.
Ether: The base unit for everyday transactions and balances.
Reading Gas Prices
When you see "gas is 30 gwei," it means each unit of gas costs 30 gwei. A simple ETH transfer uses about 21,000 gas units, so at 30 gwei: 21,000 × 30 = 630,000 gwei = 0.00063 ETH. Smart contract interactions use more gas and therefore cost proportionally more.