Wire, load, and conduit — NEC-referenced estimates for planning a circuit.
Wire sizing, voltage drop, and conduit fill are engineering questions with published answers, and the National Electrical Code is where those answers live. It is also not the last word: your jurisdiction adopts a specific edition, may amend it, and the inspector applies what it adopted. These calculators are built for the stage before that conversation — planning a circuit, pricing a run, checking whether a length is going to cost you too much voltage before you buy the wire. Results cite the Code section behind them so you can see which rule produced which number, and take the same reference to the electrician doing the work.