Paper GSM Explained: Sheet Weight Is Not Thickness
GSM means grams per square metre: paper mass divided by area. It helps compare how much paper weighs, but it does not directly measure thickness, stiffness, opacity or whether a particular printer can feed the sheet.
Estimate the mass of an A4 sheet
A4 area is 0.210 × 0.297 = 0.06237 m². At 80 GSM, one sheet has a calculated paper mass of 80 × 0.06237 = 4.9896 g, approximately 4.99 g. Five hundred such sheets have a calculated paper mass of about 2.495 kg, before packaging. Nominal dimensions and basis mass do not guarantee the measured mass of every individual sheet.
Choose stock for the actual job
| Question | What to check |
|---|---|
| Will it feed? | Printer and tray media limits, sheet dimensions and coating |
| Will writing show through? | Opacity and a sample with the intended pen or ink |
| Will it fold neatly? | Stock stiffness, grain and a folded sample |
| How thick is it? | Caliper or a measured specification, rather than GSM alone |
Why pound values need a paper grade
US basis weight uses the mass of a ream at a grade-specific basic sheet size. A 20 lb bond paper and a 20 lb cover paper do not represent the same mass per square metre. Choose the basic size as well as the pound figure before converting. A conversion without that basis can be misleading.
Use a sample before buying a large pack
Check the manufacturer’s printer compatibility and recommended media settings. A higher GSM number does not guarantee a better photo or a more reliable duplex result. Coating, absorbency and stiffness can change performance even between papers with the same nominal GSM.
Sources and method
- WCP Solutions: basis weight and GSM: paper-grade basic sizes and the difference between basis weight and mass per area.