Surface density converter

Paper is specified by grammage: ordinary office paper is 80 g/m², a magazine cover or business card 250–350 g/m². The US instead quotes basis weight, the weight in pounds of a ream of 500 sheets in the paper's basic sheet size, and that size differs by paper type, so there is no single factor. The value here uses the 25 × 38 in size of text and book papers, where 60 lb is about 89 g/m²; bond paper is based on 17 × 22 in sheets, so 20 lb bond is about 75 g/m². Fabrics are weighed in ounces per square yard: 12 oz denim is about 400 g/m².