Quick answer: The UK and most of the world use grammage in grams per square metre, while the US commonly also uses basis weight in pounds per ream of a specified parent-sheet size. Different paper grades use different US basis sizes.
This means “24 lb paper” is incomplete without the grade system. Twenty-four-pound bond and 24-pound cover are not equivalent because their basis sheets differ. GSM avoids that ambiguity by referring to one square metre for every grade.
Editorial standard: This guide distinguishes measured paper properties, trade terminology and practical advice. It cites institutional, standards-based or technical sources and avoids treating marketing terms as proof. For valuable documents, hazardous contamination or conservation treatment, use a qualified professional.
Why Are British and American Paper Weights Measured Differently? at a glance
| Check | What it means |
|---|---|
| Main answer | The UK and most of the world use grammage in grams per square metre, while the US commonly also uses basis weight in pounds per ream of a specified parent-sheet size. Different paper grades use different US basis sizes. |
| Most important variable | GSM scales directly with area. |
| Best practical step | Use GSM as the common comparison value. |
| Main risk to avoid | Comparing 80 lb text with 80 lb cover as if equal. |
Metric grammage
GSM scales directly with area. Once grammage and sheet dimensions are known, mass can be calculated. The same number has the same meaning for coated, uncoated, bond or cover stock.
US basis weight
Basis weight is the mass in pounds of a nominal ream, commonly 500 sheets, cut to the traditional basic size for that grade. Bond, text, cover, index and bristol use different basic sizes, so identical pound numbers can represent very different grammages.
Why conversion charts vary
Charts round values and may assume a specific grade. Converting 80 gsm to pounds requires choosing the correct basis system. Merchant charts are convenient, but the manufacturer’s stated GSM is safer for technical work.
How to specify internationally
Write the paper name, manufacturer, finish, GSM, thickness and grain direction. Add the US basis weight only when needed. This avoids substitutions based on a misleading pound number.
Using the specification in a real paper order
A reliable paper specification combines the mill and grade name with grammage, caliper or bulk, finish, colour, grain direction, sheet size and intended printing process. Numerical properties should include a recognised test method because the same everyday word can be measured in more than one way. Request a current technical data sheet and a production sample rather than basing a purchase on an online thumbnail or generic merchant description.
For a substantial print run, proof the most demanding content: heavy solids, fine reversed type, photographs, folds, handwriting areas and duplex pages. Confirm the press profile, drying or fusing requirements and finishing tolerances. This turns an abstract specification into evidence that the exact stock will perform in the exact job.
Practical checklist
- Use GSM as the common comparison value.
- Identify whether the US figure is bond, text, cover, index or another basis.
- Confirm ream definition and basis size in supplier documentation.
- Do not convert printer limits with a generic chart unless the grade is known.
Common mistakes
- Comparing 80 lb text with 80 lb cover as if equal.
- Calling US basis weight pounds per sheet.
- Relying on rounded conversion tables for postage calculations.
How to make a reliable decision
Paper performance depends on the finished grade, not one isolated label. When the decision affects print cost, preservation, safety or a large production run, obtain the current manufacturer data sheet, identify the test method behind numerical claims and test a representative sample under the real conditions of use. Local recycling and waste rules take precedence over general material advice.
For historic or valuable material, document the current condition before intervention. A reversible, minimal action is preferable to an aggressive treatment that improves appearance temporarily but removes original material or creates long-term chemical damage.
Frequently asked questions
What is 20 lb bond in GSM?
It is commonly around 75 gsm, but check the manufacturer’s specification.
What is 24 lb bond in GSM?
It is commonly around 90 gsm.
Why keep the US system?
It is embedded in trade practice and grade categories, even though GSM is clearer for cross-grade comparison.
Does Britain ever use pounds?
Historic and specialist trade language may, but GSM is the normal modern metric specification.
Related Paper101 guides
- Complete paper size chart
- Printer paper sizes explained
- A4 paper size guide
- Printer paper sizes explained
Sources and further reading
Sources are selected for technical authority and relevance. Standards catalogue pages identify recognised measurement frameworks; conservation sources describe preventive care rather than endorsing unsupervised treatment. Product and local-authority guidance should be checked for the exact paper and location.