How to Calculate Deck Square Footage With Angles
Decking is often constructed in rectangles. However, it may cover an unusually shaped area with odd angles instead on right-angle corners. Knowing the square footage of the decking is necessary before the build, to determine the volume of materials required, and after the build, when calculating the volume of paint or wood preservative needed to protect the decking. By dividing the decking into simple shapes and calculating the square footage of each separate area, the total square footage of decking with angles can be determined using only straightforward math.
Divide as much as possible of the decking area into rectangles. Rectangles are easy shapes for measuring areas and will simplify your calculations. For example, if the main body of the decking is in an L shape, divide it into two rectangles; if it is C-shaped, divide it into three rectangles. Mark these areas on the decking.
Measure the length and width of each rectangle in inches. Multiply the length by the width for each rectangle and record the value. The result is the surface area. For example, an area of decking formed around an L shape may include two rectangles measuring 120 by 72 inches and 108 by 72 inches. Multiply 120 by 72 and 108 by 72 to find their surface areas in square inches. The example results would be 8,640 and 7,776 square inches, respectively.
Divide the remaining area into right triangles. Any shape with straight edges can be subdivided into rectangles and triangles. The area of a right triangle is half of the base multiplied the height.
Add together the individual areas of all the rectangles and triangles. The combined total is the surface area of the decking in square inches.
For example, an area of decking consisting of two rectangles measuring 120 by 72 inches and 108 by 72 inches and a triangle measuring 36 inches by 48 inches has a surface area of 18,144 square inches -- 8,640 + 7,776 + (1,728 / 2).
Divide the total area in square inches by 144, the number of square inches in a square foot. The result is the decking area measured in square feet.
For example, a decking area of 18,144 square inches is equivalent to 126 square feet -- 18,144 / 144 = 126.
- When measuring decking with angles, it is not necessary to measure the actual angles. Doing so serves no purpose, as the angles must be converted into lengths of sides, and you can do that directly with a tape measure.
- For most construction projects, a good approximation of the area is sufficient. Wood comes in standard lengths and pack sizes, so measurements need to be rounded up to the next whole pack size anyway.
- Measurement marks made with light pencil lines or white chalk will wash off both untreated and treated wooden surfaces.
- Ensure that whatever you use to mark out measurements on the decking will not leave permanent marks.
David Robinson has written professionally since 2000. He is a Fellow of the Royal Geographical Society and the Royal Meteorological Society. He has written for the "Telegraph" and "Guardian" newspapers in the U.K., government publications, websites, magazines and school textbooks. He holds an honors Bachelor of Arts in geography and education and a teaching certificate from Durham University, England.
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