Gas is an accounting unit for execution resources, distinct from the cryptocurrency used to pay the bill. A transaction consumes gas as it performs operations, including computation, reading or changing state, and carrying transaction data. Different operations have different costs because they impose different burdens on the network. This metering prevents a single instruction sequence from demanding unlimited work from every node and gives transactions an explicit execution budget.

Suppose an ordinary transfer uses 21,000 gas and its effective execution price is 18 gwei per gas. Multiplying gives 378,000 gwei, or 0.000378 ETH. These are illustrative inputs, not a fee quote. Sending twice as much ETH in an otherwise equivalent transfer does not automatically double the gas used. Interacting with a contract can require much more work, so the transferred amount alone is a poor predictor of its execution fee.

A successful fee estimate is not an endorsement of a contract or a guarantee that a future transaction will succeed. State may change between simulation and inclusion, and an execution that reverts can still consume gas. A quoted layer-two total may also contain a separate charge for publishing data to its settlement chain. Compare the transaction receipt, the network's fee documentation, and the actions actually executed rather than treating every displayed fee as the same measurement.