Paper Weight Converter: GSM and Pounds by Paper Grade
Convert paper basis weight in pounds to GSM, or reverse the calculation, using the correct paper grade. Then estimate the mass of a finished sheet. A pound rating without its basic sheet size is incomplete; GSM alone cannot establish thickness, stiffness or printer compatibility.
Choose the basis before converting
Worked example: 20 lb bond
Choose Pounds to GSM, enter 20 and select Bond / writing, whose basic sheet is 17 × 22 inches for the 500-sheet basis used here. The result is approximately 75.195 GSM. A nominal A4 sheet at that grammage has an estimated mass of about 4.690 g.
By comparison, 80 lb cover on a 20 × 26 inch basis is about 216.329 GSM. Entering the same pound number with another grade changes the result because the area behind that rating changes.
Two rectangles with different jobs
The basic sheet defines the area used for the pound rating. The finished sheet is the piece you plan to print, such as 210 × 297 mm A4. Cutting a sheet changes the mass of each piece, but does not change the material’s GSM.
Use the Custom basis only when your supplier specifies a different basic size for 500 sheets. Editing either basic dimension changes the grade selector to Custom. The calculator does not infer a missing grade or support an unspecified ream count, packaging weight or another meaning of pounds.
Calculation method
GSM = pounds × 453.59237 ÷ (500 × basic width in inches × basic height in inches × 0.0254²). The reverse conversion uses the same area factor. Finished sheet mass in grams = GSM × width in millimetres × height in millimetres ÷ 1,000,000.
The display rounds to three decimal places. Real products have tolerances and may use nominal commercial equivalents rather than the precise arithmetic shown. For purchasing, retain the supplier’s stated specification; this calculation is an estimate, not a laboratory measurement.
Before putting heavier stock in a printer
Check the manufacturer’s supported media type, thickness, size, weight and feed path. Two stocks of equal GSM can have different bulk, coatings and stiffness. A value returned by this converter does not establish that either is safe to feed, duplex or heat in a laser printer.
Reference and related decisions
WCP Solutions explains the basis-weight system and the different basic sizes used by paper grades. PaperGridly’s formulas convert mass and area on that stated basis. Read GSM versus thickness and cardstock versus ordinary paper before choosing a material.