One confusing aspect of paper is its basis weight – the weight of a ream of paper (500 sheets) in the parent size. The parent size for bond paper is 17”x22”; for text, offset and coated papers 25”x38”; and for cover paper, 20”x26”. Each paper grade has a range of basis weights: 16#-24# for bond, 50#-70# for offset, 50#-100# for coated book, 60#-100# for text, and 60#-100# for cover. (Pounds is often indicated by using the # sign.)
Counterintuitively, the basis weight does not indicate the thickness of the paper. The thickness of paper is called the caliper, and it is measured in thousands of an inch and referred to in points. (This is different than the point size of fonts, which measures the height of characters.) One-thousandth of an inch equals one point, so ten-point paper has a thickness of 0.10 inch. Because the caliper of paper is not related to basis weight, a smaller-sized, thick sheet may have the same basis weight as a thinner paper in a larger parent size.