Gas is a kind of "fuel" of the Ethereum network. Every operation, from a simple ether transfer to executing a smart contract, requires a certain amount of computation, and this amount is measured in gas units. Simple actions consume little gas, while complex ones — for example, deploying a smart contract or interacting with a decentralized application — consume noticeably more.

The cost of gas is paid by the initiator of the transaction. The price per unit of gas is usually stated in gwei (Gwei) — this is a fractional unit of ether, where 1 ETH equals 1,000,000,000 Gwei. The final fee equals the amount of gas spent multiplied by the chosen price per unit. Transactions with a higher gas price are generally processed faster, since it is more profitable for validators to include them in a block first.

What is important to know about gas

• gas measures the computational load of an operation, not its monetary value;
• the gas price is set in gwei and affects processing speed;
• if you set the gas limit too low, execution will stop, the changes will roll back, and the fee paid for the completed part will not be refunded.

Understanding the mechanics of gas helps to calculate fees in advance and avoid overpaying by choosing a reasonable balance between the speed and the cost of a transaction.