Gwei
A tiny denomination of ether (ETH) commonly used to express gas fees. One ETH equals one billion gwei.
How it works
Gwei is not a separate coin but a convenient unit for very small amounts of ether. One ether holds a billion gwei, and one gwei holds another billion wei, the smallest fraction. The idea is the same as cents in a dollar, just with more steps.
The unit exists because an Ethereum transaction fee is measured in thousandths of a coin. Writing “0.000000021 ETH” is awkward and easy to miscount, while “21 gwei” reads at a glance.
Wallets almost always show the gas price in gwei. Multiply it by the amount of work your operation takes and you get the fee in ether.
Working out the fee
A plain ether transfer costs 21,000 units of gas. Here is what that comes to at different network loads.
| Quiet network, 8 gwei | 0.000168 ETH |
| Ordinary day, 21 gwei | 0.000441 ETH |
| Peak load, 120 gwei | 0.00252 ETH |
The gap between a quiet hour and a peak is fifteenfold. If the operation is not urgent it pays to wait: gas prices move through the day and are usually lower at night and on weekends.
What to watch for
- Gwei is a price, not a totalThe fee depends on both the gas price and the complexity of the operation. A swap on a decentralised exchange uses ten times the gas of a plain transfer, so at the same price it costs ten times more.
- Too low a price means a stuck transactionSet the price below what the network is accepting and the transfer will sit pending for hours. Wallets normally suggest a sensible value themselves.
- Layer-two networks show different figuresOn Arbitrum or Base fees are measured in fractions of a gwei. Numbers from the main network are misleading there.