How paper weight is measured
There are two systems:
- Grammage (gsm): the weight of one square meter of paper, in grams. It is used everywhere outside North America and is independent of the paper type.
- Basis weight (lb): the weight of a ream of 500 sheets cut to the “basic size” of that paper type. Because each type has a different basic size, 20 lb bond and 50 lb text are nearly the same paper.
US basis sizes and conversions
| Paper type | Basic size | 1 lb equals |
|---|---|---|
| Bond / writing | 17 × 22 in | 3.76 gsm |
| Text / book / offset | 25 × 38 in | 1.48 gsm |
| Cover | 20 × 26 in | 2.70 gsm |
| Index | 25.5 × 30.5 in | 1.81 gsm |
Common equivalents: 20 lb bond ≈ 75 gsm, 24 lb bond ≈ 90 gsm, 32 lb bond ≈ 120 gsm, 80 lb cover ≈ 216 gsm.
Example
20 lb bond, Letter size, 500 sheets:
- grammage: 20 × 3.76 ≈ 75 gsm;
- one sheet: 75.2 × 0.0603 m² ≈ 4.5 g;
- the ream: about 5 lb;
- stack height: about 1.9 in.
Postage
A USPS First-Class letter costs the base price up to 1 oz (28.35 g). With a light envelope of about 0.2 oz, you can mail about 5 sheets of 20 lb Letter paper for the base rate. Heavier paper, extra pages or a padded envelope can push the letter into the next price tier.
Choosing paper
- 20 lb bond (75 gsm): everyday copier paper.
- 24 lb bond (90 gsm): resumes and letters with a more substantial feel, less show-through.
- 28–32 lb bond (105–120 gsm): presentations and double-sided color printing.
- 65–110 lb cover (176–300 gsm): cards, covers, invitations. Check that your printer accepts the weight.
Thickness
Thickness (caliper) depends on the paper’s density, not only its weight. Office paper is about 0.004 in (0.1 mm) thick at 75 to 80 gsm. Coated papers are thinner for the same weight, and recycled or bulky papers thicker. The stack height shown is an estimate.