A transaction fee is just multiplication
Every transaction fee comes down to two numbers: how much computation it used (gas units) and how much you agreed to pay per unit (gas price). Everything else — EIP-1559’s base fee and priority fee, L2 data fees, wallet fee estimates — is ultimately about arriving at those two numbers; once you have them, the cost itself is a straight multiplication.
Why a quick manual calculation is useful
Before signing anything, or when comparing “what would this roughly cost at a calmer time”, it’s often faster to plug in a gas price and a typical gas-limit ballpark than to wait on a live estimate. It won’t be exact — your wallet’s simulation against the actual contract always will be — but it’s accurate enough for planning.
How this tool works
Your Gwei price is converted to wei and multiplied by the gas units entirely with viem’s arbitrary-precision unit handling — no floating-point rounding, all client-side.