How to Figure Roofing Supplies

Roofing supplies are commonly sold by "square" units, with one square equaling 100 square feet. There are four kinds of roofing materials to estimate: 1. Shingles; 2. Paper or felt; 3. Nails; 4. Drip edge. A few measurements and some simple math is all you need estimate each job.

• 1

  Measure the roof. Using the tape measure, determine the width and length of the roof. Measure to the nearest whole foot; using inches is unnecessary. Measure complicated roofs in sections, then add area of each section together. Also measure the perimeter of the roof.

• 2

  Calculate the roof area. Multiply the length of the roof by its width to determine the area. If you measured the roof in sections, calculate the area for each section, and add the areas together.

• 3

  Determine the number of squares required. Divide the area (in square feet) of the roof by 100; the result is the number of squares.

• 4

  Calculate materials. Shingles may be ordered by the square, but they are also sold in bundles. Common asphalt shingles come three or four bundles per square; check with your supplier. Roofing felt comes in two grades, 15- and 30-pound. The 15-pound felt contains 4.3 squares per roll, while 30-pound felt comes in 2.1-square rolls. Add the perimeter measurements together to determine the linear feet of drip edge required. Drip edge is sold in 8- or 10-foot lengths (check with your supplier). You need 1.5 pounds of 1-inch roofing nails per square, or two pounds of 1-½-inch roofing nails per square. To account for waste, add an extra two percent for simple roofs, and five percent for complex roofs.