412 Landscape Design, Installation, and Management Copyright Goodheart-Willcox Co., Inc. Calculating Materials Accurate site measurements are essential for calculating and ordering suf- fi cient hardscape materials. Accurate measurements are also important when determining the cost of a project and ensuring the work is profi table for the landscape business. The amount of materials ordered should be 5% to 10% greater than the actual estimated need for the project. Ordering additional materials will ensure a suffi cient amount for the job and it will also compen- sate for defective or broken pieces. Square Footage Many hardscape materials are sold by the square foot. You can determine the square footage of an area with standard calculations for geometric shapes, such as squares, circles, and triangles. See Figure 15-18. Irregular Shapes The most effi cient way to determine the square footage of an irregularly shaped area is to divide the area into geometric fi gures, such as rectangles, circles, and triangles, determining the square footage for each shape, and add- ing the measurements together. See Figure 15-19. w l The area of a rectangle or square is found by multiplying the length (l) by the width (w). Area = l × w Example: l = 100′ w = 50′ Area = 100′ × 50′ = 5000 ft2 r The area of a circle is calculated by multiplying the radius2 (one-half the diameter) by 3.14 (𝛑 is the symbol for pi, which is 3.14). Area = r2 × 3.14 Example: r = 100′ Area = 3.14 × (100′)2 = 31,400 ft2 w b a A trapezoid has four sides, two of which are parallel. The area is found by multiplying the average length of the parallel sides by the width. Area = [(a + b) ÷ 2] × w Example: a = 200′ b = 300′ w = 50′ Area = [(200′ + 300′) ÷ 2] × 50′ = 500′ × 50′ = 12,500 ft2 h b The area of a triangle is one-half of the base multiplied by the height. Area = 1/2 × b × h Example: b = 200′ h = 400′ Area = 1/2 × 200′ × 400′ = 100′ × 400′ = 40,000 ft2 Goodheart-Willcox Publisher Figure 15-18. Two-dimensional measurements can easily be determined by using geometric shapes and applicable equations.