What is Gwei?

See “20 Gwei” in your wallet and wondering how much you’ll pay? That number shows the price per unit of gas, not the transaction’s total cost. We use Gwei so we don’t have to write out a string of zeros every time we talk about such tiny amounts of ETH.

Think of a gas station pump: the price per gallon is one thing, and the final bill is another. On Ethereum, gas measures the computational work a transaction requires, while Gwei usually expresses how much each unit of it costs. Gas is the quantity; Gwei is the unit its price is expressed in.

For example, if a transaction consumes 21,000 units of gas and the final price is 20 Gwei per unit, the fee will be 420,000 Gwei, or 0.00042 ETH. The numbers are hypothetical: different actions require different amounts of gas.

Why it matters

When you send ETH or use a decentralized application (dApp), the fee depends both on the work required and on the gas price. A complex interaction with a smart contract can cost more than a simple transfer, even at the same price in Gwei.

On Ethereum, the final price per unit of gas includes the base fee, which adjusts according to demand for block space, and the priority fee. We find it more useful to look at the total estimated cost in ETH, not just the Gwei figure.

What to watch out for

Gwei isn’t a separate token you need to buy. It’s a way of measuring ETH, just as cents are a subdivision of the euro, but on a much smaller scale.

Also, the maximum price you allow per unit of gas isn’t necessarily what you end up paying. The gas limit refers to the amount of work you allow, not its price. If a transaction is executed but fails, the gas consumed is still charged.