Siding Calculator Formula
Understand the math behind the siding calculator. Each variable explained with a worked example.
Formulas Used
Gross Wall Area
gross_wall_area = gross_areaOpening Deductions
opening_deductions = openingsNet Siding Area
net_siding_area = net_areaSiding Needed (with waste)
siding_with_waste = net_area * (1 + waste_percent / 100)Siding Squares
siding_squares = net_area * (1 + waste_percent / 100) / 100Variables
| Variable | Description | Default |
|---|---|---|
wall_perimeter | Total Wall Perimeter(feet) | 160 |
wall_height | Wall Height(feet) | 9 |
num_doors | Number of Doors | 3 |
num_windows | Number of Windows | 12 |
waste_percent | Waste Factor(%) | 10 |
gross_area | Derived value= wall_perimeter * wall_height | calculated |
openings | Derived value= num_doors * 21 + num_windows * 15 | calculated |
net_area | Derived value= gross_area - openings | calculated |
How It Works
How to Calculate Siding
Formula
Net Area = (Perimeter × Height) - (Doors × 21 sq ft) - (Windows × 15 sq ft)
Siding Needed = Net Area × (1 + Waste %)
Siding is often sold in "squares" (100 sq ft). Vinyl siding panels typically cover about 2 squares (200 sq ft) per box. Lap siding exposure varies by product.
Worked Example
A house with 160 ft perimeter, 9 ft walls, 3 doors, 12 windows, 10% waste.
- 01Gross area = 160 × 9 = 1,440 sq ft
- 02Openings = 3 × 21 + 12 × 15 = 63 + 180 = 243 sq ft
- 03Net area = 1,440 - 243 = 1,197 sq ft
- 04With 10% waste = 1,197 × 1.10 = 1,317 sq ft
- 05Siding squares = 1,317 / 100 = 13.2 squares
Frequently Asked Questions
How much siding do I need for a 1,500 sq ft house?
A 1,500 sq ft ranch-style house typically has about 1,200-1,500 sq ft of wall area (after deducting openings). With waste, plan for 1,300-1,650 sq ft of siding, or 13-17 squares.
What is a square of siding?
One square = 100 square feet of wall coverage. This is the standard ordering unit for siding, similar to roofing.
How long does vinyl siding last?
Quality vinyl siding lasts 20-40 years. Fiber cement siding (e.g., HardiePlank) lasts 30-50 years. Wood siding can last 20-40 years with proper maintenance.
Learn More
Guide
How to Calculate Roofing Materials: Shingles, Underlayment, and More
Learn how to calculate roofing materials including shingles, underlayment, flashing, and ridge caps. Covers roof area measurement, pitch factors, and waste allowances.
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