How many square shingles for 16'x20' roof?

To calculate the number of square shingles needed for a 16'x20' roof, first find the total area by multiplying the length by the width: 16 x 20 = 320 square feet. One square of shingles covers 100 square feet, so divide the total area by 100: 320 ÷ 100 = 3.2 squares. Therefore, you would need approximately 4 squares of shingles to account for waste and cuts.