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GSM and US basis weights
Paper weight is measured in two different systems, and converting between them causes constant confusion. Most of the world uses GSM, grams per square metre: the weight of one square metre of the paper. A higher GSM means heavier, thicker paper. The United States uses basis weights in pounds: the weight of 500 sheets of a standard-size sheet for that grade of paper. The catch is that the standard sheet size differs by grade. Bond paper uses a 17 by 22 inch sheet, cover stock uses 20 by 26 inches, and text paper uses 25 by 38 inches. That is why one paper has three different US weights: the same sheet weighs differently when the reference sheet size changes.
This converter turns GSM into US bond, cover and text weights, and turns any US weight back into GSM. The conversions use standard factors: one pound of bond is about 3.76 GSM, one pound of cover is about 2.70 GSM, and one pound of text is about 1.48 GSM. These are industry approximations, not mill specifications, because real papers vary slightly by manufacturer.
How to use the converter
- Enter the paper weight in GSM to see all three US weights at once.
- Or choose a US weight type, enter the pounds, and convert back to GSM.
- Compare the result with the paper you have: office paper, book paper and card behave very differently.
A worked example
Take 100 GSM paper. The converter shows about 26.6 pounds bond, 37 pounds cover and 67.6 pounds text. All three numbers describe the same paper. If a US supplier lists a paper as 100 pound cover, converting back gives about 270 GSM, which is a sturdy card suitable for a book cover or a premium postcard. If a supplier lists 100 pound text, converting back gives about 148 GSM, which is a thick text paper for a quality brochure. The grade name matters as much as the number, and mixing up cover and text weights is the most common ordering mistake.
Office copy paper shows the other end of the scale. Standard copy paper is 75 to 80 GSM, which is 20 to 21 pounds bond. It feeds reliably through printers, folds easily, and costs little. A business card, by contrast, is often 350 to 400 GSM, which is roughly 130 pounds cover. Holding those two papers explains GSM instantly: the copy paper feels thin and flexible, and the business card feels stiff and substantial. GSM is not just a number on a spec sheet; it is the feel of the paper in the hand.
Choosing a paper weight
- 75 to 90 GSM: everyday printing, letters, invoices and drafts.
- 100 to 120 GSM: letterheads, reports and quality documents.
- 130 to 170 GSM: flyers, brochures and magazine pages.
- 200 to 250 GSM: premium brochures, menus and thin covers.
- 250 to 400 GSM: covers, business cards, postcards and packaging.
Heavier is not always better. Very heavy paper can jam a home printer, crack on a fold unless it is scored, and add postage cost to a mailing. Match the weight to the job: light paper for things people read and throw away, heavy paper for things people keep. When in doubt, ask the printer for samples at two or three weights and compare them in the hand. The converter tells you what the numbers mean, but the sample tells you what the paper feels like.
Weight, thickness and stiffness
GSM measures weight, not thickness. Two papers at the same GSM can have different thicknesses, because a bulky uncoated paper is thicker than a dense coated paper of the same weight. That thickness, called caliper, is what the paper thickness calculator on this site estimates from GSM and density. Stiffness is a third property again: a coated card feels stiffer than an uncoated sheet at the same GSM. For most buying decisions, GSM is the right starting number, and caliper matters when the paper must fold, feed through a machine, or fit a spine. The spine width calculator uses caliper directly, which is why converting GSM to thickness is a step worth doing before a book cover is designed.
Related calculators
- Spanish version
- Paper Size Converter – A, B and C Series Dimensions in Millimetres and Inches
- Paper Thickness Caliper Calculator – Sheet Thickness from GSM and Density