What Is a Siding Calculator?
A siding calculator estimates how much exterior siding you need to cover a building's walls. In the construction industry siding is sold and measured in squares, where one square equals 100 square feet of coverage. This tool converts your wall dimensions into squares so you can order the right amount of material and avoid costly extra trips to the supplier.
How to Use It
Enter the combined width of all the walls you plan to cover, the average wall height, and the total area of any openings such as doors and windows (so you are not paying to side over them). Add a waste allowance — typically 10% for simple walls and up to 15% for cut-up walls with many corners, gables, or angles. The calculator returns your net wall area, the raw number of squares, and the recommended order quantity with waste included.
The Formula Explained
First the net wall area is found: \(\text{wallArea} = (\text{width} \times \text{height}) - \text{openings}\). That area is divided by 100 to convert square feet into siding squares: \(\text{squares} = \text{wallArea} \div 100\). Finally the waste factor is applied: \(\text{order} = \text{squares} \times (1 + \text{waste\%})\).
$$\text{Squares} = \frac{\left(\text{Wall Width} \times \text{Wall Height}\right) - \text{Openings}}{100} \times \left(1 + \frac{\text{Waste \%}}{100}\right)$$
Worked Example
Suppose your walls total 40 ft wide and 10 ft tall, giving 400 sq ft, with 60 sq ft of doors and windows. Net wall area is \(400 - 60 = 340\) sq ft. Dividing by 100 gives 3.4 squares. Adding a 10% waste allowance: \(3.4 \times 1.10 = 3.74\) squares, so you would order about 3.74 squares (round up to 4 when purchasing).
FAQ
What is a "square" of siding? It is 100 square feet of finished coverage — the standard unit siding is sold by.
How much waste should I add? Use about 10% for plain rectangular walls and 15% for walls with many windows, corners, or gables.
Should I include the gable triangles? Yes — add the gable area to your total wall area for an accurate estimate.
