Gas & Fees

This page explains how zksync-js quotes deposit gas and fees.

Source Of Truth

The protocol constants and validator rules used by the SDK come from era-contracts:

The SDK mirrors those constants in code, but the contracts above are the protocol source of truth.

Deposit Quotes

Deposit quotes are conservative caps, not realized post-execution charges.

fees.l2.gasLimit is the quoted L2 execution budget used to price the priority transaction.
fees.l2.baseCost is the result of Bridgehub.l2TransactionBaseCost(...) for that budget.
fees.l2.total = fees.l2.baseCost + operatorTip.
fees.maxTotal = fees.l1.maxTotal + fees.l2.total.
fees.mintValue is the amount funded into the Bridgehub request. For direct base-token deposits, it includes the transferred L2 value as well as the quoted L2 fee reserve.

That means explorer gasUsed and realized L2 fee can be lower than the quote.

Deposits

Direct Deposits: `eth-base` and `erc20-base`

Direct deposits use the exact canonical priority-transaction encoding and the validator floor from TransactionValidator.

The SDK computes the exact abi.encode(L2CanonicalTransaction) length for the direct request shape, then applies:

minBodyGas =
  max(
    L1_TX_INTRINSIC_L2_GAS +
      ceilDiv(encodedLength * L1_TX_DELTA_544_ENCODING_BYTES, 544),
    L1_TX_MIN_L2_GAS_BASE,
  ) +
  L1_TX_INTRINSIC_PUBDATA * gasPerPubdata

overhead =
  max(
    TX_SLOT_OVERHEAD_L2_GAS,
    MEMORY_OVERHEAD_GAS * encodedLength,
  )

l2GasLimit = minBodyGas + overhead

This is the quoted cap for direct deposits unless the caller explicitly overrides l2GasLimit.

Two-Bridges Asset-Router Deposits: `erc20-nonbase` and `eth-nonbase`

For non-base asset-router deposits, the quote depends on whether the bridged asset is already deployed on L2.

When the bridged asset already exists on L2, the SDK asks L1AssetRouter.getDepositCalldata(...) for the exact L2 finalize-deposit calldata, computes the exact canonical priority-transaction encoding length, and applies the same validator-floor formula shown above.

This keeps the quote asset-specific because calldata length depends on the actual bridge payload.

First Deployment Path

For undeployed erc20-nonbase and eth-nonbase deposits, exact deployment-path estimates can fluctuate across environments and underquote the real L2 execution. The SDK therefore uses a calibrated dynamic cap derived from the validator floor instead of trusting the exact estimate:

bodyGas = minBodyGas * 6
l2GasLimit = bodyGas + overhead

This still scales with the exact calldata length and gasPerPubdata, but avoids environment-specific low estimates on first deployment.

Base Cost Pricing

After the route chooses l2GasLimit, the SDK prices it with:

baseCost = Bridgehub.l2TransactionBaseCost(
  chainId,
  l1GasPrice,
  l2GasLimit,
  gasPerPubdata,
)

So the gas-limit model and the gas-price model are separate:

l2GasLimit is the execution budget.
l1GasPrice and gasPerPubdata determine how that budget is priced.

Manual Overrides

If you pass l2GasLimit, the SDK uses your override instead of the route-specific model.

This is useful for controlled environments, but for general-purpose quoting the built-in route models are safer because they align with the current deposit path and protocol validator rules.

ZKsync SDK