Electrical & Plumbing Calculators
Sizing before shopping: the wire a circuit needs, the tank a household needs, and the septic capacity a bedroom count implies.
There are 3 calculators here: Romex Wire Footage & Cost Calculator (wire footage, rolls and cost for a branch circuit run), Septic Tank & Drain Field Sizing Calculator (tank size, drain field area and system cost by bedroom count), and Water Heater Sizing & Operating Cost Calculator (tank size from household demand, and what it costs to run).
They all work the same way: quantity first, then a waste allowance you can change, then a price built from verified figures and adjusted for your state. Cost is always a range rather than a single number, and every assumption behind it is printed on the page with its source and the date it was last checked.