Smart Contract Gas Estimator

Transaction cost = gasUsed × gasPrice. Gas price = baseFee + priorityFee (EIP-1559). baseFee is burned by the protocol and fluctuates with demand. priorityFee (tip) goes to the validator. Gas limit is the maximum gas you're willing to spend — unused gas is refunded. Total ETH cost = gasUsed × (baseFee + priorityFee).

ETH transfer: 21,000 gas. ERC-20 transfer: ~65,000 gas. ERC-20 approve: ~46,000 gas. Uniswap V3 swap: ~130,000-200,000 gas. NFT mint (ERC-721): ~100,000-200,000 gas. Contract deployment: 200,000+ gas depending on bytecode size. Storage write (SSTORE): 20,000 gas. Storage read (SLOAD): 2,100 gas.

L2s (Arbitrum, Optimism, Base, zkSync) execute transactions off the main Ethereum chain and only post compressed data to L1. This reduces costs 10-100x. Optimistic rollups have ~7-day withdrawal delays but are EVM-equivalent. ZK rollups use validity proofs for instant finality. Most DeFi activity has moved to L2s for cost reasons.

EIP-1559 (London upgrade, 2021) replaced the first-price auction with a base fee + tip model. The base fee is algorithmically set by the protocol based on demand and is burned (removed from supply). The tip (priority fee) is optional and goes to validators. This makes fee prediction more reliable and reduces fee overpayment.

Key optimizations: (1) Pack storage slots — multiple small variables in one slot. (2) Use calldata instead of memory for read-only inputs. (3) Cache storage reads in memory variables. (4) Use mappings over arrays for lookups. (5) Avoid dynamic array loops with unbounded size. (6) Use custom errors instead of require strings. (7) Use immutable/constant for deploy-time values.