One bundle of shingles covers approximately 33 square feet of roof, depending on the size and weight of the shingles. Typically, it takes three bundles of standard-sized, standard-weight shingles to cover 100 square feet of roof surface.
Bundles are packaged at a weight that is light enough for one person to carry easily. This means that heavier materials may be packaged with fewer shingles per bundle, resulting in a bundle that covers less surface space.
A better way to determine how many shingles are needed is to measure the roof and divide the measurement by 100 square feet. A square of shingles covers 100 square feet, so they are sold by the square, not by the bundle.