Siding Calculator – Hardie Board, Plank & Lap Siding
Calculate how much siding you need for your project. Free siding calculator for James Hardie, vinyl, and wood siding materials.
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Siding Calculator Formula
Net Area = (Wall Height × Wall Width × Number of Walls) - Openings Area
How to Calculate Siding
- 1. Measure the height and width of each wall in feet
- 2. Calculate total wall area: height × width × number of walls
- 3. Subtract the area of all doors and windows
- 4. Add waste factor (typically 10%) for cuts and mistakes
- 5. Divide by 100 to get the number of squares
Example Calculation
Let's say you're calculating siding for a house with four 10ft × 40ft walls, 80 sq ft of openings, and 10% waste.
- wallHeight: 10
- wallWidth: 40
- numWalls: 4
- openingsArea: 80
- wasteFactor: 10
Total area = 1,600 sq ft, minus 80 sq ft openings = 1,520 sq ft net, plus 10% waste = 1,672 sq ft (16.72 squares)
Tips
- Siding is sold in 'squares' — one square equals 100 square feet
- Always add 10-15% waste factor for cuts, mistakes, and future repairs
- Hardie plank siding comes in 12ft lengths with various widths (5.25", 6.25", 7.25", 8.25")
- Measure each wall separately for the most accurate estimate
Frequently Asked Questions
How do I calculate how much siding I need?
Measure each wall's height and width, multiply to get area, subtract door and window areas, then add 10-15% for waste. Divide the total by 100 to get squares.
How much Hardie plank siding do I need?
Calculate your net wall area in square feet, add 10% waste, then divide by 100 for squares. A typical 1,500 sq ft home needs about 15-17 squares of siding.
How many pieces of Hardie siding are in a square?
The number depends on the plank width. For 8.25-inch wide planks, approximately 18 pieces cover one square. For 6.25-inch planks, about 24 pieces per square.