By using simple calculations you can estimate the number of roof shingles that will be needed to complete the job. Roofs come in many shapes and sizes and can be classified into simple geometric shapes such as squares, rectangles, trapezoids and triangles. To determine how many shingles will be needed you must calculate the area of the roof. This is done by figuring out what geometric shapes make up your roof, calculating the area of the individual shapes and summing the areas to give you the total area of the roof. The area required is then divided by the area each bundle covers. Don’t forget to add allowances for ridges, starter strips, etc.