The weight of a ream of paper depends on how thick the sheets are. A 500-sheet pack of 20-pound bond paper weighs 5 pounds, while a 500-sheet pack of 24-pound bond paper weighs 6 pounds.
In the United States, bond paper comes in sheets that are 17 inches by 22 inches and are cut into four letter-size sheets. The pound number for each type of paper is based on how much 500 sheets of that type of paper weigh.
For example, 500 sheets of 20-pound paper weigh 20 pounds. The weight of each type of paper is based on how much fibre is used to make it. Newsprint paper weighs 18 pounds, while printmaking and painting papers weigh 300 pounds.