There are 27 shingles per bundle with the in/ft system, three bundles per roofing square, or 100 sq. ft. You have to consider exposure, not actual size. Exposure is 5 inches s … o you have 5 x 36 inches =180 sq.Inches divided into 14,400 sq. inches (120 x 120) = 80 shingles divided by three = 26.66 shingles per bundle.ow divide by 100 since there are 100 sq foot in one Square. =17 square. Now multiply the number of Square by the number of bundles required to cover one Square 17 x 3 = 51 bundle of shingle. Other tips, one bundle of 3-tab shingles will cover about 25 lineal feet when used for cap.