Most of the world measures paper in grams per square metre (g/m², often written GSM). It is a simple density: a one-metre square sheet of 80 g/m² paper weighs 80 grams, whatever kind of paper it is.
North America uses basis weight: the weight in pounds of 500 sheets of the paper's basic size. The catch is that the basic size differs by grade.
Why the same paper has different pound weights
| Grade | Basic sheet | 1 lb ≈ |
|---|---|---|
| Bond / writing | 17 x 22 in | 3.76 g/m² |
| Text / book / offset | 25 x 38 in | 1.48 g/m² |
| Cover | 20 x 26 in | 2.70 g/m² |
| Index | 25.5 x 30.5 in | 1.81 g/m² |
Because a ream of text-grade sheets is much larger than a ream of bond sheets, the same paper weighs more as "text". That is why ordinary 75 g/m² copy paper is called 20 lb bond but would be about 50 lb text. Use the converter or the chart to translate between them.
Weight is not thickness
Grammage tells you mass, not caliper. A bulky uncoated book paper can be noticeably thicker than a smooth coated sheet of the same weight. Thickness is what determines spine width, so printers quote caliper (in points or micrometres) or pages per inch alongside weight.
Typical weights for books
- Novel and nonfiction interiors: roughly 50–60 lb text (74–90 g/m²), white or cream, uncoated.
- Mass-market paperbacks: lighter groundwood papers, around 40–50 lb text (55–70 g/m²).
- Colour interiors and photo books: 70–100 lb text (100–150 g/m²), often coated.
- Paperback covers: 10–12 pt C1S board (roughly 220–300 g/m²) with gloss or matte lamination.
- Bibles and reference works: very thin "India" papers of 25–40 g/m².
Choosing between white and cream
Cream paper is easier on the eyes for long reading and is the convention for most fiction; white gives sharper contrast for images, charts and colour and is the default for nonfiction and textbooks. Cream is usually bulkier, so the same book has a wider spine.