Squares, the siding unit
Like roofing, siding is ordered in <strong>squares of 100 square feet</strong>. The calculator takes the wall perimeter × height, subtracts doors and windows, and converts to squares with a 10% waste allowance for starter strips, corner trims and the cuts around every opening.
Gables and stories change the math
Triangular gable ends add roughly half their base × height each — measure them separately and add. Two-story houses save money per square foot because the wall is continuous, but require staging: scaffolding rental is a real line item that scales with height, not area.