How to Estimate Siding Accurately

Siding Estimate Calculator
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You need square feet of siding.
(Includes a 5% waste factor.)

When building a new home, or remodeling the exterior, you need to obtain accurate estimates for all of your building costs. Many home building materials are charged by the square foot, including siding. If you want to accurately compute the amount of siding, use the guide below. It requires nothing more than knowledge of simple geometry. We describe two methods of estimation that yield the same figures. You can also use the convenient siding estimate calculator on the left.

Method 1

For the first method, sketch your house showing the house from four different directions: front, back, and the two sides. With a pencil, shade the rectangular and triangular panels that need siding.

Next, find the area of each rectangle by multiplying width and height. To find the area of each triangle, multiply width times height times 1/2. Now add up all of these areas to get the total siding area. Call this number X.

Now, subtract the total area of any outside doors, windows, and garage doors that don't require siding. Call this number Y. The total area that needs siding is X-Y.

Multiply the total area times the cost per square foot of siding.

For example, suppose the total side of your house is 3100 square feet, the total area of outside windows and doors is 260 square feet, and cost per square foot of siding is $1.45. Then your siding estimate would be about (3100-260)(1.45) = $4118.

Method 2

There is another way to estimate the siding area of your home's exterior, without having to add the areas of individual rectangles. First, find the perimeter of your home, and multiply that number times the height. (Height is measured as the distance from the ground to the base of the roof.)

For example, if the perimeter of your home is 246 feet around, and the height is 9.5 feet, then the total area of all the rectangular sections is (246)(9.5) = 2337 square feet.

Of course, you still need to calculate the areas of the triangular sections under the gables, as well as subtract the area of windows and doors.

© Had2Know 2010