Paper weight converter (lb ↔ gsm)
"80 lb" means different paper depending on the grade. Enter a weight and pick its unit to see the same paper in gsm and in every US grade.
Converter
| Same paper expressed as | Value |
|---|
What do the sheets weigh?
How the conversion works
Grams per square metre (gsm, also written g/m²) is the mass of one square metre of the paper. ISO 536 defines grammage this way.[5] It does not depend on sheet size, so 90 gsm is 90 gsm everywhere.
The US pound number is different. It is the weight of one ream of 500 sheets cut to that grade's basic size, and each grade has its own basic size.[1] A ream of 80 lb cover is weighed at 20 × 26 in. A ream of 80 lb text is weighed at 25 × 38 in, a much bigger sheet. So the same "80 lb" label covers two very different papers.
To convert, the tool divides the ream weight in grams by the ream area in square metres:
gsm = lb × 453.59237 ÷ (500 × width_in × height_in × 0.00064516)
453.59237 g is the exact international pound and 0.00064516 m² is exactly one square inch (1 in = 25.4 mm exactly).[3] The part after lb × is a fixed factor for each grade:
| Grade | Basic size[1] | gsm per lb |
|---|---|---|
| Bond, writing, ledger, copy paper | 17 × 22 in | 3.7597 |
| Text, book, offset | 25 × 38 in | 1.4801 |
| Cover | 20 × 26 in | 2.7041 |
| Index | 25.5 × 30.5 in | 1.8080 |
| Tag, newsprint | 24 × 36 in | 1.6275 |
| Bristol | 22.5 × 28.5 in | 2.1928 |
Printed charts round these factors to 3.76, 1.48, 2.70, 1.81, 1.63 and 2.19.[1][2] This tool uses the unrounded values, so it can differ from a chart by about 1 gsm.
To go from one US grade to another, the tool converts to gsm and back: lb_B = lb_A × factor_A ÷ factor_B. The sheet-weight box multiplies gsm by the sheet area in square metres and by the number of sheets. A-series sizes come from ISO 216.[4]
Worked examples
- 20 lb bond (everyday copy paper). The basic size is 17 × 22 = 374 in², or 0.241290 m². A ream is 500 sheets, so 120.645 m². Then 20 lb × 453.59237 g = 9,071.85 g, and 9,071.85 ÷ 120.645 = 75.2 gsm. Charts usually print 75 gsm.[1]
- 80 lb cover. 80 × 2.7041 = 216.3 gsm (charts: 216 gsm).[1]
- 80 lb text. 80 × 1.4801 = 118.4 gsm (charts: 118 gsm). That is a little over half as heavy as 80 lb cover.
- 110 lb index as cover weight. 110 × 1.8080 = 198.9 gsm, and 198.9 ÷ 2.7041 = 73.5 lb cover, between 70 lb and 80 lb cover.
- A 300 gsm card in US terms. 300 ÷ 2.7041 = 110.9 lb cover. Bindrite's table lists 300 gsm next to 111 lb cover.[2]
- Ten Letter sheets of 75 gsm. One sheet is 8.5 × 11 = 93.5 in² = 0.0603225 m², so ten sheets are 0.603225 m² × 75 = 45.2 g (1.60 oz).
Where answers go wrong
- The grade is missing. "100 lb paper" can be about 148.0 gsm (text) or 270.4 gsm (cover). Ask which grade, or ask for gsm.
- Real paper varies. The industry standard allows basis weight to vary by ±5%, so a ream of 20 lb bond can really be 19 to 21 lb (about 71 to 79 gsm).[1]
- Weight is not thickness. Caliper (thickness, in points or mils) depends on coating and density. Two papers with the same gsm can feel quite different, and gsm cannot be converted to points.
- "Cardstock" is not a grade. Card is usually sold as cover or index weight. Check which one the seller means before you compare.
- Other systems are not covered. Japan's ream-weight (kg per 1,000 sheets) system and paperboard caliper ratings are separate and not converted here.
- Sheet weights are paper only. For postage, add envelopes, ink, stamps and inserts, and weigh the finished piece if you are near a limit.
Common questions
Is 24 lb bond the same as 60 lb text?
Nearly. 24 lb bond is 90.2 gsm and 60 lb text is 88.8 gsm, so they are within about 1.5 gsm of each other, closer than the ±5% mill tolerance.
Why does my chart say 16 lb bond is 61 gsm when this says 60.2?
Charts round. Xerox's table lists 61,[1] and Bindrite's lists 60.[2] The exact formula gives 60.2.
Which is heavier, 65 lb cover or 110 lb index?
110 lb index is heavier: 198.9 gsm against 175.8 gsm for 65 lb cover.
Sources
- Xerox Support, "Convert Paper Weight From Pounds (lbs) to Grams Per Square Meter (gsm)," KB0328426 (basic sizes, multipliers, ±5% tolerance, equivalents table). support.xerox.com/en-us/article/KB0328426. Checked 2026-10-24.
- Bindrite, "Paper Weight Conversion Table" (PDF; conversion factors 3.760, 1.480, 2.704, 1.808, 2.193, 1.627). bindrite.com (PDF). Checked 2026-10-24.
- NIST Special Publication 811, Appendix B.9, "Factors for units listed by kind of quantity" (inch = 2.54 × 10−2 m exactly; pound (avoirdupois) = 0.45359237 kg exactly, listed rounded as 4.535 924 × 10−1 kg). nist.gov. Checked 2026-10-24.
- ISO 216:2007, "Writing paper and certain classes of printed matter: Trimmed sizes, A and B series" (standard page; A4 = 210 × 297 mm, A5 = 148 × 210 mm, A3 = 297 × 420 mm). iso.org/standard/36631.html. Checked 2026-10-24.
- ISO 536:2019, "Paper and board: Determination of grammage" (standard page; defines grammage in g/m²). iso.org/standard/77583.html. Checked 2026-10-24.
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