Siding Calculator Formula

Understand the math behind the siding calculator. Each variable explained with a worked example.

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Formulas Used

Gross Wall Area

gross_wall_area = gross_area

Opening Deductions

opening_deductions = openings

Net Siding Area

net_siding_area = net_area

Siding Needed (with waste)

siding_with_waste = net_area * (1 + waste_percent / 100)

Siding Squares

siding_squares = net_area * (1 + waste_percent / 100) / 100

Variables

VariableDescriptionDefault
wall_perimeterTotal Wall Perimeter(feet)160
wall_heightWall Height(feet)9
num_doorsNumber of Doors3
num_windowsNumber of Windows12
waste_percentWaste Factor(%)10
gross_areaDerived value= wall_perimeter * wall_heightcalculated
openingsDerived value= num_doors * 21 + num_windows * 15calculated
net_areaDerived value= gross_area - openingscalculated

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.

wall_perimeter = 160wall_height = 9num_doors = 3num_windows = 12waste_percent = 10
  1. 01Gross area = 160 × 9 = 1,440 sq ft
  2. 02Openings = 3 × 21 + 12 × 15 = 63 + 180 = 243 sq ft
  3. 03Net area = 1,440 - 243 = 1,197 sq ft
  4. 04With 10% waste = 1,197 × 1.10 = 1,317 sq ft
  5. 05Siding squares = 1,317 / 100 = 13.2 squares

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