The thickness or quality of paper used for a book’s interior pages. Paper is measured in pounds per ream (500 sheets) of standard-sized sheets of paper measuring 17 x 22″, which is later cut into quarters to produce “letter-size”. If a standard-sized ream weighs 20-pounds, it would make the paper “20-lb paper”, which is the average weight for office copy paper. Our paper comes in Standard 50 lb in white or creme, or Premium 70 lb.