To calculate the number of shingle course on a roof, follow the formula below:
Number of Courses = Width of Roof Section (eave to ridge along common rafter)/Exposure
Example: Calculate the number of courses of 12-inch-wide asphalt shingles required to cover the roof below. Assume a slope of 6 in 12 and 5-inch exposure.
On the roof plan, the distance from the eave to the ridge is 20’. We use the table below to identify the actual distance
Note: before dividing, we must standardize our units. They must be both inches or feet. Let’s multiply the numerator (22.36’) times 12 to convert it to inches.
22.36 x 12 / 5 = 53.66 or 54 Courses.
This means that one of the two sections of the roof has 54 courses since the other section is exactly the same, we simply multiply times 2 to get the total number of courses. 54 x 2 = 108