Understanding Calldata: The Hidden Gas Cost Most Developers Overlook

One of the most underrated parts of gas optimization in Solidity is calldata — the raw bytes your contract receives as input. Every single byte in calldata costs gas, and unlike memory or storage operations, calldata is charged per byte, not per operation.

Each calldata byte has a cost:

• Zero byte → 4 gas

• Non-zero byte → 16 gas

This means simply passing more data automatically increases the transaction cost.

Fun Fact:

Your Ethereum address actually affects gas usage.

Addresses with more leading zeros are cheaper to pass it as a function argument (encoded in calldata) — meaning two users calling the exact same function can pay different gas fees simply because their address bytes contain different amounts of zeros. Wild, right?

Calldata vs Memory vs Storage:

• Calldata: charged per byte

• Memory: charged per word (32 bytes), but cheaper than calldata per byte

• Storage: extremely expensive compared to both

Understanding these differences helps you choose the right data location and structure.

Contract design impacts user gas fees:

Forcing users to send large arrays, long strings, or unnecessary parameters means they must pay more — not because of your logic, but because of the calldata size.

How to reduce calldata cost:

• Minimize input sizes

• Prefer fixed-size types over dynamic ones

• Pack data efficiently

• Avoid unnecessary parameters

• Use hashing techniques when possible instead of sending raw data

These small details add up. A few bytes saved in calldata can lead to meaningful gas reductions, especially in high-traffic protocols.

If you want a deeper understanding of ABI encoding and calldata behavior, I highly recommend reading the original RareSkills article by Eze Sunday Eze:

https://rareskills.io/post/abi-encoding