ScrollL2: How to Caculate L1Fee

• tags: Ethereum Layer 2

Background

You may meet the below error when you’re trying to transfer all your ETH from one address to another address:

invalid transaction: insufficient funds for l1fee + gas * price + value

The reason is that the Layer 1 fee are included in Scroll’s gas fee system, but the wallet only exclude the Layer 2 gas fee to do so when you transfer all your ETH. ¹

How the L1 Fee be Caculated?

1. Some state is stored in the state store slots², which including:

   • l1BaseFee
   • precision
   • overhead
   • scalar

2. You got some RLP³ encoded raw data when you send tx to Scroll, which need to be stored to the Layer 1 network as a calldata, which requires fee charge⁴. let’s name it:

   • raw

3. Finally we put all these together⁵

   // EIP-1559
   // 16 * non-zero calldata bytes + 4 * zero calldata bytes
   l1GasUsed = calcCalldataFee(calldata) + overhead
   l1Gas = round((l1GasUsed * l1GasPrice * scalar) / precision)
   

How to Retrieve State Slots?

L1BaseFeeSlot

POST https://alpha-rpc.scroll.io/l2
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": 40,
  "method": "eth_getStorageAt",
  "params": [ "0x5300000000000000000000000000000000000002", "0x1"]
}

OverheadSlot

POST https://alpha-rpc.scroll.io/l2
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": 40,
  "method": "eth_getStorageAt",
  "params": [ "0x5300000000000000000000000000000000000002", "0x2"]
}

ScalarSlot

POST https://alpha-rpc.scroll.io/l2
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": 40,
  "method": "eth_getStorageAt",
  "params": [ "0x5300000000000000000000000000000000000002", "0x3"]
}

In a Batch

POST https://alpha-rpc.scroll.io/l2
Content-Type: application/json

[
  {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "eth_getStorageAt",
    "params": [ "0x5300000000000000000000000000000000000002", "0x1"]
  },
  {
    "jsonrpc": "2.0",
    "id": 2,
    "method": "eth_getStorageAt",
    "params": [ "0x5300000000000000000000000000000000000002", "0x2"]
  },
  {
    "jsonrpc": "2.0",
    "id": 3,
    "method": "eth_getStorageAt",
    "params": [ "0x5300000000000000000000000000000000000002", "0x3"]
  }
]