Siding Square Footage and Waste Factor Calculator
Calculate the total siding material needed for your project, including a waste factor to account for cuts, overlaps, and mistakes.
Formula
Step 1 — Gross Wall Area (sq ft)
Gross Wall Area = (Total Wall Length × Wall Height) + Gable Area
Step 2 — Net Wall Area (sq ft)
Net Wall Area = Gross Wall Area − Total Openings Area
Step 3 — Total Siding Needed (sq ft)
Total Siding = Net Wall Area × (1 + Waste Factor ÷ 100)
Step 4 — Squares
Squares = Total Siding ÷ 100 (1 square = 100 sq ft)
Assumptions & References
- Wall length should be the total perimeter length of all walls to be sided.
- Gable area for a triangular gable = ½ × base × height.
- Openings (doors and windows) are fully subtracted; increase the waste factor if many small cuts are expected around openings.
- A square is the standard unit for siding: 1 square = 100 sq ft. Source: National Association of Home Builders (NAHB).
- Waste factor recommendations: 5–10% for straight runs; 10–15% for complex layouts or diagonal patterns; up to 20% for very complex designs. Source: This Old House / James Hardie installation guidelines.
- Always purchase slightly more than calculated and round up to the nearest full square to avoid shortages from dye-lot or batch differences.
- This calculator does not account for siding exposure width, starter strips, trim boards, or J-channel — consult your siding manufacturer's installation guide for those adjustments.