Siding Calculator

Gross wall area (sq ft). Measure the wall faces receiving siding before subtracting openings. Add rectangular sections and other measured wall areas as needed. This is wall surface area, not floor area or the projected footprint of the building.

Opening deductions (sq ft). Enter the square-foot area of doors, windows or other surfaces you choose to exclude from the siding takeoff. Consider the installation and cutting pattern before deducting every small opening. The deduction cannot be larger than the gross wall area.

Waste allowance (%). Enter the percentage you want to add for cutting, handling loss or other conditions specific to this work. Apply it to the measured quantity rather than enlarging the measurements as well. The suggested value is editable, not a universal recommendation; enter zero when no allowance is needed.

Purchasing unit. Choose whether you purchase this siding by panels, individual pieces or cartons. The name changes how you interpret the quantity; the coverage entered below must describe one of that same purchasing unit.

Effective coverage per unit (sq ft). Use the effective installed coverage of one selected panel, piece or carton. Exposure and overlap can make this smaller than its raw face area. Check the product information and do not deduct the same overlap again as waste.

Net wall area is gross area minus the openings you entered. Required coverage includes waste. The purchasing count rounds up to whole selected units, and purchased coverage is the area those units cover. Trim, corners, flashing and other accessories need separate takeoffs.

Net area = gross wall area − opening deductions.
Required coverage = net area × (1 + waste ÷ 100).
Purchasing units = round up(required coverage ÷ effective coverage per unit).

Worked example: 1,000 sq ft gross minus 100 sq ft of openings gives 900 sq ft net. With 10% waste, allow 990 sq ft. A product covering 20 sq ft per carton requires 50 cartons, covering 1,000 sq ft.

Effective coverage varies with product exposure, overlap, and installation. Trim, corners, accessories, and product-specific details are excluded. Check manufacturer specifications and opening-deduction practice.