How to use the paper weight converter (lb to gsm)
- Choose to convert pounds to gsm or gsm to pounds.
- Enter the paper weight, such as 20 for 20 lb paper or 90 for 90 gsm paper.
- Pick the paper type, or choose a custom basic size and enter its width and height in inches.
- Read the converted weight and the table that shows the same weight for every basic size.
Formula
Area of 500 sheets = 500 x width x height square inches x 0.00064516 square meters per square inch
gsm = pounds x 453.59237 / area of 500 sheets
Pounds = gsm x area of 500 sheets / 453.59237
Basis weight in pounds is the weight of 500 sheets cut to the basic size of the paper type, and gsm is grams per square meter.
20 lb bond paper
20 lb bond uses a basic size of 17 x 22 inches. 500 sheets cover 500 x 374 = 187,000 square inches, which is 120.64 square meters. 20 pounds is 9,071.85 grams, and 9,071.85 / 120.64 = 75.19 gsm. One pound of basis weight is 3.7597 gsm.
The same 20 lb is 29.6 gsm in text, 54.1 gsm in cover and 32.5 gsm in tag, because the basic sizes differ. In the other direction, 90 gsm bond is 23.9 lb, and 100 gsm is 37.0 lb cover.
Why the same pounds mean different paper
In the United States, paper is graded by the weight of 500 sheets of a basic size, and the basic size depends on the paper type. So a 20 lb sheet of bond and a 20 lb sheet of cover are very different paper, because 20 lb cover is measured on a much smaller basic sheet. Grams per square meter does not depend on type, so it is the common ground.
That is why you must choose a paper type before converting. The table shows the same number read for each type, which helps when a supplier lists weights in a type you do not use.
Checking the basic sizes
The basic sizes in the table are an example reference. They are the sizes commonly quoted for these paper types, and the table is there so that you can see exactly what the tool uses, but sizes can differ by mill or country, so confirm with your paper supplier. For an unusual stock, choose the custom option and enter the supplier's basic size.
Weight is not thickness. Caliper, finish and brightness are separate properties. For sheet dimensions, see the paper size converter, and for page counts the word count to pages converter. The unit converter handles general weights.
Assumptions and limits
- Basic sheet sizes are an example table. Confirm with your supplier.
- Constants used: 1 pound is 453.59237 grams and 1 inch is 0.0254 meters.
- Results are rounded for display.
- Thickness, finish and brightness are not part of weight.
Frequently asked questions
How do I convert pounds to gsm for paper?
Multiply the pounds by 453.59237 and divide by the area of 500 basic sheets in square meters. This tool does it for each paper type, because the basic size changes with the type.
Why does 20 lb paper not always equal 75 gsm?
Only bond paper uses the 17 x 22 inch basic size that gives 75 gsm. Other paper types use other basic sizes, so the same pounds give a different gsm.
What is basis weight?
It is the weight in pounds of 500 sheets cut to a basic size, which differs for each paper type. It is how paper is graded in the United States.
What if my paper has a different basic size?
Choose the custom option and enter the width and height from your supplier, and the tool will convert using that size.