Paper Weight (GSM) Calculator
US paper weights are famously confusing, because a number like twenty pound bond means something different from twenty pound cover, and this paper weight calculator clears it up by converting to grams per square meter, the universal GSM measure used almost everywhere else. The reason for the confusion is that US basis weight is the weight of a ream of 500 sheets cut to each grade's own standard basis size, and those sizes differ by grade, so the same pound figure does not represent the same actual paper weight across bond, text and cover. GSM sidesteps the problem entirely by stating grams per square meter regardless of sheet size. To use the calculator, enter the US basis weight in pounds and the conversion factor for your paper grade, and the tool multiplies the two to give the GSM. Bond and writing paper use a factor of about 3.7606, text and book grades about 1.4805, and cover stock about 2.7048, so the factor is left editable to match whatever grade you are working with. The result lets you compare papers fairly by weight and feel. The method is a single multiplication, shown in the formula below, with a worked example that reconciles exactly to the calculator defaults.
GSM is the US basis weight scaled by a grade factor: GSM = pounds x conversion factor. A 20 pound bond paper, using the bond factor of 3.7606, converts to about 75.21 GSM.
Paper weight GSM formula
GSM = B x F
B = US basis weight in pounds
F = conversion factor for the paper grade
Bond F = 3.7606, text F = 1.4805, cover F = 2.7048
The conversion factor folds in the grade's basis sheet size, so multiplying the pound figure by the right factor gives grams per square meter directly.
Worked example
You have 20 pound bond paper and use the bond conversion factor of 3.7606.
- GSM = basis weight x factor
- GSM = 20 x 3.7606
- GSM = 75.21
The paper is about 75.21 GSM. These are the calculator's default inputs, so the result above matches the widget exactly.
Common grade conversion factors
| Grade | Factor (lb to GSM) |
|---|---|
| Bond / writing | 3.7606 |
| Text / book | 1.4805 |
| Cover | 2.7048 |
| Index | 1.8083 |
| Tag | 1.6275 |
Factors reflect each grade's standard US basis sheet size.
Paper weight GSM calculator: frequently asked questions
How do I convert paper pounds to GSM?
Multiply the US basis weight in pounds by the conversion factor for the paper grade. For bond and writing paper the factor is about 3.7606, so 20 pound bond is 20 x 3.7606, which equals roughly 75.21 grams per square meter. GSM is a universal weight measure because it is grams per square meter regardless of the sheet size used to define the US basis weight.
Why are US paper pounds confusing?
US basis weight is the weight of 500 sheets (a ream) of paper cut to that grade's standard basis size, and the basis size differs by grade. Bond is based on a 17 by 22 inch sheet, while cover and text grades use different sizes, so the same pound number means different actual weights across grades. GSM avoids this by measuring grams per square meter directly.
What conversion factor should I use?
The factor depends on the paper grade. Bond and writing paper use about 3.7606, text and book grades about 1.4805, and cover stock about 2.7048, among others. Because the factor changes with grade, this calculator leaves it as an editable input. Enter the factor for your specific paper to get an accurate GSM.
Is GSM the same as thickness?
No. GSM measures weight per area, not thickness. Two papers can share the same GSM but differ in caliper (thickness) depending on how the fibers are pressed and the bulk of the sheet. For thickness you need a separate caliper measurement, often given in mils or microns. GSM is best for comparing weight and feel across grades.
What is the paper weight GSM formula?
GSM equals the US basis weight in pounds multiplied by the grade conversion factor. With 20 pound bond and a factor of 3.7606, that is 20 x 3.7606, which equals about 75.21 grams per square meter.
Official sources
- Weight and measurement standards: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.