Quick guide
How to convert paper weight
- Choose which number you know: GSM, grade-specific basis lb, or cut-sheet M-weight.
- If you use basis lb, select the correct paper grade; each grade has its own basic sheet size.
- Select the cut-sheet size and enter your sheet count to calculate M-weight, ream weight, and your job's total.
- Use the equivalent table as a weight comparison only. Check a manufacturer's actual stock specifications before substituting paper.
Why GSM and basis lb differ
GSM is the mass in grams of one square meter of paper. A US basis weight is the weight in pounds of 500 sheets at a grade's basic size. That size is 17 × 22 inches for Bond/Writing, but 25 × 38 inches for Text/Book. The same GSM therefore produces different basis-lb numbers in those categories.
For example, 20 lb Bond is about 75.2 GSM by exact arithmetic. The same mass per area is about 50.8 lb Text—not a 20 lb Text stock. Actual catalog labels commonly round these values.
What is M-weight?
M-weight is the weight in pounds of 1,000 sheets at the selected cut size. It changes when you change the cut dimensions even if the paper grade and GSM stay the same. A 500-sheet cut-size ream is half the M-weight. Here “ream” always means exactly 500 cut sheets; check your package count if it differs.
A4 dimensions are exactly 210 × 297 mm in this calculator. US Letter is 8.5 × 11 inches. Switching the display unit preserves the physical dimensions.
Paper weight formulas
Area (m²) = width (in) × height (in) × 0.0254²Basis lb = GSM × basic-sheet area (m²) × 500 ÷ 453.59237GSM = basis lb × 453.59237 ÷ (basic-sheet area × 500)M-weight lb = GSM × cut-sheet area (m²) × 1,000 ÷ 453.59237Job weight lb = GSM × cut-sheet area (m²) × sheet count ÷ 453.59237To start from M-weight, solve the M-weight equation for GSM, then calculate the chosen grade's basis lb. The displayed numbers are rounded; calculations use the unrounded values. This estimates paper mass only, excluding packaging, ink, coatings added after the stated grammage, and production waste.
Basic-size reference
| Grade | Basic sheet |
|---|---|
| Bond / Writing | 17 × 22 in |
| Text / Book | 25 × 38 in |
| Cover | 20 × 26 in |
| Index | 25.5 × 30.5 in |
| Tag | 24 × 36 in |
| Vellum Bristol | 22.5 × 28.5 in |
These conventional basic sizes are different from the physical cut sheets used for M-weight. Use “Custom basic size” if your supplier specifies another basis size.
Frequently asked questions
Is 80 lb Text the same as 80 lb Cover?
No. Text and Cover have different basic sheet sizes. 80 lb Text is about 118.4 GSM; 80 lb Cover is about 216.3 GSM. They also may differ in finish and handling.
Can GSM tell me paper thickness in points or mils?
No. GSM measures mass per area. Caliper measures thickness; density, fiber, coating, and manufacturing affect it. Ask the supplier for a caliper specification or sample.
Why does my supplier's GSM differ slightly?
Published paper weights are often nominal and rounded; actual stock tolerances may also apply. The calculator uses exact dimensional arithmetic and the entered nominal weight, so it may not reproduce a catalog's rounded equivalent exactly.
Does M-weight depend on paper grade?
Only indirectly. Once GSM and the physical cut-sheet size are known, M-weight is simply the mass of 1,000 such sheets. The grade changes the basis-lb label, not the physical mass for a fixed GSM and cut size.
Are my calculations uploaded?
No calculator inputs are submitted or stored. The result is calculated in your browser; copy or print it if you need a record.
References
The Paper Mill Store's basis-weight and grammage explainer describes the 500-sheet basic-size convention and 17 × 22-inch Bond size. Its M-weight explainer defines M-weight as 1,000 cut sheets, and its basic-size guide lists Text, Book, Cover, Index, and Bristol dimensions. Neenah's paper stock list shows Index, Tag, and Bristol products with their basis labels, GSM, caliper, and M-weights.