Estimating Transaction Fees on OP Mainnet

It's important to properly estimate the cost of a transaction on OP Mainnet before submitting it to the network. Here you'll learn how to estimate both of the components that make up the total cost of an OP Mainnet transaction, the execution gas fee and the L1 data fee. Make sure to read the guide on Transaction Fees on OP Mainnet for a detailed look at how these fees work under the hood.

Execution Gas Fee

A transaction's execution gas fee is exactly the same fee that you would pay for the same transaction on Ethereum. This fee is equal to the amount of gas used by the transaction multiplied by the gas price attached to the transaction. Refer to the guide on Transaction Fees on OP Mainnet for more information about the execution gas fee.

When estimating the execution gas fee for a transaction, you'll need to know the gas limit and the max fee per gas (opens in a new tab) for the transaction. Your transaction fee will then be the product of these two values. Refer to the guide on Setting Transaction Gas Parameters on OP Mainnet to learn how to select an appropriate gas limit and max fee per gas for your transaction.

// Start with your parameters
gas_limit = 420000
base_fee_per_gas = 0.05 gwei
priority_fee_per_gas = 0.1 gwei
 
// Max fee per gas is the sum of the base fee and the priority fee
max_fee_per_gas = base_fee_per_gas + priority_fee_per_gas = 0.15 gwei
 
// Execution gas fee is the product of the gas limit and the max fee per gas
execution_gas_fee = gas_limit * max_fee_per_gas = 420000 * 0.15 gwei = 0.000063 ETH

L1 Data Fee

The L1 data fee is a fee paid to the Sequencer for the cost of publishing your transaction to Ethereum. This fee is paid in ETH and is calculated based on the size of your transaction in bytes and the current gas price on Ethereum. Refer to the guide on Transaction Fees on OP Mainnet for more information about the L1 data fee.

Unlike the execution gas fee, the L1 data fee is an intrinsic fee for every transaction. This fee is automatically charged based on the size of your transaction and the current Ethereum gas price. You currently cannot specify a custom L1 data fee for your transaction.

Tooling

Several tools are available to help you estimate the L1 Data Fee for your transaction. Selecting the right tool for your use case will depend on your specific needs.

• Viem (opens in a new tab) provides first-class support for OP Stack chains, including OP Mainnet. You can use Viem to estimate gas costs and send cross-chain transactions (like transactions through the Standard Bridge system). It's strongly recommended to use Viem if you are able to do so as it will provide the best native support at the moment.
• If you are using Ethers v5, the Optimism SDK (opens in a new tab) provides methods for estimating the L1 Data Fee for your transactions and for sending cross-chain transactions. The Optimism SDK is designed to be used alongside Ethers v5 and does not yet support Ethers v6.
• If you are using Ethers v6, the Optimistic Utilities Extension (opens in a new tab) provides methods for estimating the L1 Data Fee. The Ethers v6 extension does not yet support sending cross-chain transactions. Use Viem or the Optimism SDK if you need to send cross-chain transactions.

Future Proofing

The L1 Data Fee formula is subject to change in the future, especially as the data availability landscape evolves. As a result, it's important to future proof your transaction fee estimation code to ensure that it will continue to function properly as the L1 Data Fee formula changes.

• Use existing tooling to estimate the L1 Data Fee for your transaction if possible. This tooling will be updated to reflect any changes to the L1 Data Fee formula. This way you won't need to modify your code to account for any changes to the formula.
• Use the getL1Fee method on the GasPriceOracle if you are unable to use existing tooling. The getL1Fee method will be updated to reflect any changes to the L1 Data Fee formula. It's strongly recommended that you do not implement the L1 Data Fee formula yourself.