How siding quantities are calculated
Siding covers the exterior walls of a house, sold by the square — 100 square feet of wall area. Wall area equals the house perimeter (2 × length + 2 × width) multiplied by wall height, minus doors and windows. Add 10% waste for cuts, then divide by 100 for squares.
In practice, siding installers rarely deduct windows: they need material around every opening for trim and corners, and the cut-outs are small. Deduct only large openings like garage doors, and use the waste allowance as your safety margin. Gable ends add extra area — measure triangular gables separately and add half the base × height.
Siding facts
- 1 square = 100 sq ft of wall coverage
- A typical two-story home exterior: 30-40 squares
- Trim, soffit and fascia are ordered separately