Crypto glossary
Layer 2 fees
Layer 2 fees are what users pay on rollups: a charge for executing the transaction on the L2 plus a share of the cost of posting data to the base layer.
A transaction on a rollup has two main cost components. The execution fee covers the computation on the layer 2 itself and is set by the sequencer, usually with a base fee that rises when the network is busy. The data fee covers the rollup's share of publishing transaction data to the layer 1, typically Ethereum, so that anyone can reconstruct the chain. ZK rollups also spread the cost of generating and verifying proofs.
For years the data component dominated, because rollups wrote their data into ordinary Ethereum calldata. The Dencun upgrade of March 2024 introduced blobs, a separate and cheaper space for this data, and fees on major rollups fell sharply. That is why simple transfers on popular L2s usually cost a small fraction of the same action on mainnet.
L2 fees are not always low. Blob space has its own fee market that can spike, a popular mint or airdrop can congest a single rollup, and some chains post data to cheaper alternative layers with weaker guarantees. Sequencers also keep a margin, which is part of how rollup operators earn revenue.
Example
A token swap on an L2 might show a total fee of a few cents, of which most pays for execution on the rollup and a small part covers the blob space used to post the batch on Ethereum.