Paper Weight Calculator: GSM to lb Conversion
Paper weight is expressed in two incompatible systems that cause persistent confusion for anyone ordering print work or buying paper across borders. Most of the world uses GSM (grams per square metre), a clean metric standard. The United States uses three separate ream-weight systems: bond (for office and writing paper), text (for books and magazines), and cover (for thick card stock), each based on a different standard sheet size. This means the same physical paper can be described as 80 GSM, 21 lb bond, 55 lb text, or 30 lb cover depending on who is measuring. This calculator converts a GSM value into all three US systems simultaneously, calculates the actual weight per sheet (in grams) for both A4 and US Letter sizes, and then works out the total weight for however many sheets you specify. A comprehensive reference table at the bottom covers the most common paper weights from 60 to 350 GSM, showing all equivalent values and typical uses.
80 GSM = -- lb bond
Conversion formulas
The following conversion factors are standard US paper weight equivalences used by the paper and printing industry:
GSM to US cover (lb) = GSM × 0.370
GSM to US text (lb) = GSM × 0.146
Weight per A4 sheet (g) = GSM × 0.0623
Weight per US Letter sheet (g) = GSM × 0.0603
Total weight (g) = weight_per_sheet × number_of_sheets
The per-sheet weight formula comes directly from the definition of GSM: multiply grams per square metre by the sheet area in square metres. A4 is 0.210 m x 0.297 m = 0.06237 m2 (rounded to 0.0623). US Letter is 0.2159 m x 0.2794 m = 0.06032 m2 (rounded to 0.0603).
Common paper weights reference table
This table covers the most common paper weights and their equivalents across all three US weight systems:
| GSM | Bond / Writing | Text / Book | Cover | Common use |
|---|---|---|---|---|
| 60 | 16 lb | 40 lb | 22 lb | Lightweight copy / newsprint |
| 75 | 20 lb | 51 lb | 28 lb | Standard office copy paper |
| 80 | 21 lb | 55 lb | 30 lb | Standard copy / print paper |
| 90 | 24 lb | 61 lb | 33 lb | Quality office / writing paper |
| 100 | 27 lb | 67 lb | 37 lb | Premium writing paper |
| 120 | 32 lb | 81 lb | 44 lb | Light card, postcards |
| 160 | 43 lb | 107 lb | 59 lb | Brochures, flyers |
| 200 | 53 lb | 134 lb | 74 lb | Heavy card stock |
| 250 | 67 lb | 170 lb | 92 lb | Premium business cards |
| 300 | 80 lb | 202 lb | 111 lb | Heavy cover / card stock |
| 350 | 93 lb | 236 lb | 130 lb | Greetings cards, premium postcards |
Paper weight calculator: frequently asked questions
What is GSM in paper?
GSM stands for grams per square metre. It is the international metric standard for measuring paper weight. A sheet of paper that has an area of one square metre and weighs 80 grams is rated at 80 GSM. The higher the GSM, the heavier and typically thicker the paper. Standard office copy paper is 75 to 80 GSM; premium writing paper is 90 to 100 GSM; cardstock is 160 GSM and above.
Why does the US use different paper weight systems?
The United States uses ream-based weight systems where the weight is measured as the pounds per 500 sheets (a ream) at a specific standard sheet size that differs by paper category. Bond and writing paper uses a 17x22-inch base sheet; text or book paper uses 25x38 inches; cover paper uses 20x26 inches. Because the base sheet sizes differ, the same physical paper has a different lb number in each system, which is why conversions are needed.
What is the difference between bond, text, and cover weight?
Bond (also called writing) weight is used for stationery, office paper, and forms. Text (or book) weight is used for book pages, magazines, and flyers. Cover weight is used for book covers, postcards, business cards, and other thick stock. The same sheet of paper expressed in all three systems will have three different lb numbers due to the different base sheet sizes each system uses.
How is sheet weight calculated from GSM?
GSM literally means grams per square metre. To find the weight of one sheet, multiply the GSM by the sheet area in square metres. An A4 sheet is 0.0623 m2 (210 mm x 297 mm), so an A4 sheet of 80 GSM paper weighs 80 x 0.0623 = approximately 4.98 grams. A US Letter sheet is 0.0603 m2 (8.5 x 11 inches), so the same paper weighs 80 x 0.0603 = approximately 4.82 grams per sheet.
What GSM should I choose for different printing projects?
For standard office printing and photocopying, 75 to 80 GSM is sufficient. For letterheads and correspondence, 90 to 100 GSM gives a quality feel. Brochures and marketing materials work well at 130 to 170 GSM. Business cards typically use 300 to 400 GSM. Postcards are usually 250 to 350 GSM. Greetings cards are commonly 200 to 300 GSM.
Sources and methodology
- Conversion factors are standard US paper weight equivalences based on TAPPI (Technical Association of the Pulp and Paper Industry) test methods and industry-standard ream sizes. Reference: TAPPI.
- Bond factor 0.266, cover factor 0.370, and text factor 0.146 reflect the ratios of the standard ream sheet areas to the square-metre basis.
- Sheet area values: A4 = 0.0623 m2; US Letter = 0.0603 m2 (calculated from standard dimensions).
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. Conversion values are approximations based on standard industry factors; actual paper weight may vary slightly by manufacturer. See our methodology.