Vinyl is ordered by the square, installed by the course
Vinyl siding comes in 12-foot lengths covering about <strong>100 square feet per carton (one square)</strong>, installed course by course from the starter strip. The calculator converts wall area to squares; courses = wall height ÷ exposure (usually 4–5 inches), and each course needs J-channel at every edge and opening.
Leave room to move
Vinyl expands and contracts more than any other cladding — nails stay centered in the slots and never tight, panels are butted with a 1/4-inch gap, and the sheet is never stretched tight during installation. The 10% waste in the calculation also covers the panels that crack in cold-weather installs.