I just received a question from a friend about what gas fees are, so I want to share it again so everyone can understand this concept.

Gas fees are actually the costs you pay to perform any action on the blockchain, from sending tokens to executing smart contracts. Each transaction consumes computing resources, and miners have to bear this cost. Therefore, in exchange for verification work, they receive gas fees from users.

The interesting thing is that gas fees are not always the same. They vary depending on the blockchain you use. Ethereum consumes ETH, BNB Chain consumes BNB, each network has its own token. And whether the transaction succeeds or fails, you still have to pay the fee because miners have to verify and process it.

But why do gas fees fluctuate? There are two main reasons. First is the complexity of the transaction. If you execute a smart contract with many complex steps, it will consume more gas. Second is network congestion. When the blockchain is overloaded, there will be a backlog of pending transactions. At that time, miners tend to prioritize transactions with higher fees, causing gas prices to spike.

To better understand what gas fees are, you can try sending ETH via MetaMask. On the confirmation screen, you'll see an estimate of the current gas fee and can choose to speed up by paying a higher fee. After sending, use Etherscan to check the final gas fee by entering the transaction hash.

The formula for calculating transaction fees is very simple: Transaction Fee = Gas Limit × Gas Price.

Gas price is the amount of tokens you're willing to pay per unit of gas. On Ethereum, people use Gwei (1 Gwei = 0.000000001 ETH). If you set the gas price to 20 Gwei, you pay 0.00000002 ETH per gas unit. Want your transaction to be confirmed quickly? Increase the gas price. Want to save costs? Lower the gas price, but it will take longer to confirm.

Gas limit is the maximum amount of gas you're willing to spend on a transaction. This is a way to protect yourself from errors in smart contracts. For a standard transaction, the gas limit is 21,000. If you don't provide enough gas, the transaction will fail with an Out of Gas status, but the gas used will still be deducted and awarded to the miner.

The easiest way to visualize this is to compare it to car fuel. Gas limit is like the liters of fuel your car needs. Gas price is like the price per liter. If you drive from Hanoi to Saigon needing 21,000 liters, at 20 dong per liter, the cost is 21,000 × 20 = 420,000 dong. Similarly, ETH transaction fee is 21,000 (gas limit) × 20 Gwei (gas price) = 420,000 Gwei = 0.00042 ETH.

In summary, what is a gas fee? It’s a mechanism to keep the blockchain network running, motivate miners, and prevent malicious transactions. If your transaction is urgent, set a high gas price. If not in a hurry, a moderate gas price is enough. Understanding this mechanism will help you manage your transaction costs more effectively on any blockchain.