Siding calculator
List your walls, gables, windows and doors to get the net siding area, squares and the number of lap boards or cartons, plus starter and trim lengths.
Up to 300 rows and 100,000 characters, widths up to 1,000 m, heights up to 100 m and counts from 1 to 1,000, exposure up to 600 mm (23.6 in), board length up to 10 m, carton coverage up to 100 m² and waste from 0 to 50%. Calculated on your device; download a JSON report, a results CSV and a wall surfaces CSV. One row per line: type (wall, gable or opening), name, width, height and an optional count. Up to 100,000 characters. Review the settings before running.
Your result
How to use Siding calculator
- Enter one row per line: wall, gable or opening, a name, the width and height, and an optional count.
- Choose the wall dimension unit and whether the siding is sold as lap boards or by carton area.
- Enter the exposure and board length, or the coverage per carton, and the waste allowance.
- Review the net area, squares and pieces, then download the report and CSV files.
Useful next steps
Net wall area
Walls are rectangles, gables are triangles of base × height ÷ 2, and windows and doors are subtracted. Fine Homebuilding uses the same break-down into rectangles and triangles for roofs (Mike Guertin, How to Estimate Materials for Roofing Projects, checked 16 October 2026). In the example, 1,420 ft² of walls and gables less 160.5 ft² of openings leaves 1,259.5 ft².
Boards from exposure
A lap board covers only its exposure, the visible reveal after the overlap, times its length. An 8.25 in plank laid with a 7 in exposure in 12 ft lengths covers 7 ft², so 1,259.5 ft² plus 10% waste needs 198 boards. For vinyl cartons or sheet panels, enter the net coverage per carton or the face area of one panel instead.
Squares and trim
Siding is often priced by the square, 100 ft² (Wikipedia, Square (unit), checked 16 October 2026). The starter strip length is the total width of the wall rows, opening trim is the perimeter of each opening, and gable trim is both sloped edges of each gable from the Pythagorean theorem (OpenStax Precalculus 2e, 5.4, checked 16 October 2026).
Limits
Corner posts, soffits, fascia and house wrap are not included, and exposure and coverage are product-specific, so check the product literature. Unit conversions use NIST SP 811.