GSM vs lb: paper weight explained
Anyone who orders printed inserts, labels or cartons from both US and international suppliers runs into the same confusion: one quotes 100 lb cover, another quotes 270 gsm. They're close to the same paper, but you'd never guess it from the numbers.
What GSM means
GSM is grams per square meter: the weight of a one-meter square sheet. It's simple and consistent: a higher number always means heavier paper, regardless of paper type. Most of the world uses it.
What pounds mean
US paper weight is the weight in pounds of 500 sheets (a ream) of that paper at its "basis size". The trouble is that the basis size differs by paper category:
| Category | Basis size | 1 lb ≈ |
|---|---|---|
| Bond (writing, copy) | 17 × 22 in | 3.76 gsm |
| Text / book | 25 × 38 in | 1.48 gsm |
| Cover | 20 × 26 in | 2.70 gsm |
| Index | 25.5 × 30.5 in | 1.81 gsm |
So 80 lb text is about 118 gsm, while 80 lb cover is about 216 gsm. Same number, very different paper.
Common equivalents
- 20 lb bond ≈ 75 gsm (standard copy paper)
- 100 lb text ≈ 148 gsm (heavy flyers, brochure pages)
- 100 lb cover ≈ 270 gsm (postcards, thank-you cards, hang tags)
- 130 lb cover ≈ 350 gsm (premium cards)
For packaging, think in caliper
Paperboard for cartons is usually specified by thickness rather than weight: points in the US (thousandths of an inch) or microns elsewhere. Two boards of the same weight can differ in thickness and stiffness depending on how they're made. For folding cartons, ask for caliper, typically 16 to 24 pt.
Tips when ordering
Always confirm both the weight and the category ("100 lb cover", not "100 lb"). Ask international suppliers for GSM, and ask for a physical sample for anything where feel matters, like thank-you cards or presentation inserts.