How the fees are calculated on Arbitrum

The fee market in Arbitrum works a bit differently to the L1 - it is inspired by EIP 1559 but adapted to fit the L2 requirements (https://developer.offchainlabs.com/docs/inside_arbitrum#arbgas-and-fees). There is a base cost of getting your transaction processed. If demand for L2 resources are high, the base cost rises. If demand is low, it decreases.

The gas price submitted in a transaction only represents the maximum you are willing to pay, the value actually charged will depend on network congestion, similar to a 2nd price auction (read more at https://developer.offchainlabs.com/docs/inside_arbitrum#price-for-arbgas).

Querying the eth_gasPrice RPC method is a reliable gas price oracle for Arbitrum, it returns the current minimal gas price to have your transaction processed.