The Wall Siding Calculator calculates how much siding or cladding you need for a house: the wall area plus gable triangles, minus doors and windows, plus waste.
It shows the result in square feet (or m²) and in siding “squares” (100 ft² each). For lap siding, enter the exposure (the visible height of each board) and board length to get the number of boards.
Wall Siding Calculator
Siding or cladding area, squares and lap-siding boards for house walls and gables.
Formula
- Area: (P × H + gables × ½ × w × h − openings) × (1 + waste %)
- Squares: area ÷ 100 ft²
- Lap boards: ⌈area ÷ (exposure × board length)⌉
Where P = house perimeter, H = wall height to the eaves, w and h = gable width and height.
How the Calculation Works
Step 1: Multiply the perimeter by the wall height.
Step 2: Add each gable triangle and subtract doors and windows.
Step 3: Add waste, convert to squares, and divide by the area each lap board covers.
Variables Explained
| Input | Meaning |
|---|---|
| House perimeter | Total length of the exterior walls |
| Wall height | Foundation to the eaves |
| Gables | Number, width and height of triangular gable ends |
| Lap exposure | Visible face height of each board (0 for panels) |
Example Calculation
Given: perimeter 140 ft, walls 9 ft, two gables 28 ft wide and 7 ft high, 150 ft² of openings, 10% waste, 6 in exposure, 12 ft boards
Walls: 140 × 9 = 1,260 ft²; gables: 2 × ½ × 28 × 7 = 196 ft²
Net: 1,260 + 196 − 150 = 1,306 ft²; with waste: 1,436.6 ft²
Result: ≈ 14.4 squares; 1,436.6 ÷ (0.5 × 12) ≈ 240 lap boards
Common Conversion Table
| Unit | Equivalent |
|---|---|
| 1 square | 100 ft² ≈ 9.29 m² |
| 1 m² | 10.7639 ft² |
Material Estimation Notes
Trim, corner posts, J-channel, starter strips, soffit and fascia are ordered separately by length. Board exposure depends on the product and is listed by the manufacturer.
Waste Factor Considerations
Houses with many corners, gables, dormers or openings create more offcuts. The right allowance depends on the siding type and the house shape.
Frequently Asked Questions
How do you calculate siding for a house?
Wall area plus gables, minus openings, plus waste.
What is a square of siding?
100 square feet of wall coverage.
How many lap siding boards do I need?
Area ÷ (exposure × board length).
Do I subtract windows and doors?
Yes, for large openings; add them back if you want extra material.
How do I measure a gable?
Width at the base and height from the eaves to the peak; area = ½ × width × height.