Vinyl siding is sold by the square (100 ft²) in boxes that cover about two squares each. This view assumes a 10% waste factor; bump it toward 15% if your walls have several gables or dormers.
Field notes
Waste climbs with corners, not square footage. A plain gable end runs 10%; a house with dormers, bays, and multiple gables can waste 15% because every angled cut leaves an unusable offcut. Measure each wall separately and subtract only the big openings — trying to net out every window invites a shortfall. Buy one extra square and keep it for storm repairs; dye lots shift between orders.
How the vinyl siding calculator works
The math behind the tool:
wall area ft² = Σ(wall height × wall length) − openings
squares = wall area ÷ 100 × (1 + waste%)Sources: Polymeric Exteriors Alliance (formerly Vinyl Siding Institute) (siding coverage and installation standards).