There are many different types of shingles on the market. The "standard" 3-tab Owens Corning Classic 20 year shingle weighs approximately 66 pounds per bundle. There are 22 shingles per bundle, and it takes 3 bundles to cover one square of roof (100 square feet). The Berkshire series put out by Owens Corning averages about 360 pounds per square, has nine shingles per bundle, and there are 5 bundles to the "square". Not since the late 1970's have companies sold shingles by weight - they market shingles by "year" nowadays. In other words, 20 year shingles, 25 year shingles, 30 year shingles, 40 year shingles and 50 year shingles. Depending on your climate, the 20 shingle can last as long as 20 years, or as short as 14 years. Like I said, lots of choices, good luck!