Paper weight conversion chart (GSM ⇄ lb)
The same sheet of paper can be honestly labeled 80# or 216 gsm depending on which category name the mill uses. Here is the exact relationship, so you can compare stocks across systems.
The conversion factor for every stock type
| Paper category | Basic size (500-sheet ream) | GSM per pound | Example |
|---|---|---|---|
| Bond / copy / ledger | 17 × 22 in | 3.760 | 20# = 75 gsm |
| Book / offset / text | 25 × 38 in | 1.480 | 70# = 104 gsm |
| Cover | 20 × 26 in | 2.704 | 80# = 216 gsm |
| Index bristol | 25½ × 30½ in | 1.808 | 90# = 163 gsm |
| Tag board | 24 × 36 in | 1.627 | 100# = 163 gsm |
Multiply pounds by the factor to get GSM; divide GSM by it to get back. Both directions are exact because they come straight from the definition:
gsm = lb × 453.59237 g ⁄ (500 sheets × basic-area-in² × 0.00064516 m²/in²)
Common stocks at a glance
| Rating | GSM | Typical use |
|---|---|---|
| 20# bond | 75 | Copy paper, letterhead |
| 24# bond | 90 | Brochures, good letterhead |
| 28# bond | 105 | Brochures, good letterhead |
| 32# bond | 120 | Brochures, good letterhead |
Frequently asked questions
Why does basis weight depend on the paper type?
'Pound' ratings weigh one ream (500 sheets) of the paper cut to that category's basic size — and each category has a different basic size. A 20 × 26 inch sheet of cover stock simply has more fiber per sheet than a 17 × 22 inch bond sheet at the same thickness rating, so equal pound numbers are unequal grams per square meter.
Is 80# text thicker than 40# bond?
No, and it is not close: text converts at about 1.48 gsm per pound (80# → 118 gsm) while bond converts at about 3.76 (40# → 150 gsm), so 40# bond is the heavier sheet despite carrying half the number. This is exactly why comparing pound ratings across categories misleads.
What GSM is normal office copy paper?
Standard US copy paper is 20# bond, which works out to 75 gsm; European offices buy it labeled directly as 80 gsm, which is 21–22# bond. Card-stock territory starts around 160–200 gsm (roughly 60–74# cover).
Basic sizes are the North American industry standards (bond 17×22, book 25×38, cover 20×26, index 25.5×30.5, tag 24×36 inches); conversions computed exactly from those definitions. Mill tolerance applies to actual shipments.