Gas is used to pay for transactions on the Ethereum blockchain. The amount of gas required for each transaction depends on the complexity of the transaction. A simple transfer may use as much as 21,000 gas whilst a more complex transaction (for instance, those used in decentralized finance) could use in excess of 1,000,000 gas.
Each unit of gas has a price, simply referred to as the “gas price”. Gas prices are denoted in gwei, where 1 ETH = 1* 10^9 (1,000,000,000) gwei. With a gwei price of 5, a 21,000 gas transaction would cost 21,000 * 5 = 105,000 gwei (0.000105 ETH).
While the amount of gas required for any given transaction remains constant, the gas price is dynamic. Users set the gas price when sending a transaction (this is often done automatically by wallet software) and transactions are then sent to the “mempool” for Ethereum miners to include in the next block. Miners are rewarded with the transaction fees inside a block and are therefore motivated to prioritize transactions with the higher gas price.
This incentive structure leads to an auction-style market where users bid up the gas price as a means to ensure that their transaction is picked up by a miner and settled quickly.
All things being equal:
If the price of ETH increases, the average gas price decreases and vice versa. If the demand for settlement on Ethereum increases, so does the average as price and vice versa.
These two market conditions are what lead to the dynamic gas price that we see today.