GSM vs Lb Paper Weight – Cardstock Print

GSM and lb paper weight both describe paper mass, but they do so through different systems. GSM measures grams per square meter, regardless of sheet size or paper category. A U.S. pound rating usually reports the weight of a ream of full-size basis sheets, and that basis size changes between categories such as text and cover paper. That is why 80 lb text and 80 lb cover are not equivalent stocks.

For the cleanest comparison, start with GSM and confirm whether the pound value refers to text, cover, bond or another category. Then check caliper, stiffness, surface and the limits of the intended printer or finishing process. Weight is useful, but it cannot tell you by itself how thick, rigid, writable or foldable a sheet will be.

What GSM measures

GSM means grams per square meter, also written as g/m². It expresses grammage: the mass of a sheet divided by its area. The standardized area makes GSM useful when comparing papers sold in different sheet sizes or markets. The TAPPI grammage test method defines grammage as weight per unit area.

A 300 GSM stock therefore has more mass per square meter than a 200 GSM stock. That comparison remains valid even if one product is sold as a small card sheet and the other as a large press sheet. It does not, however, guarantee that the 300 GSM product is proportionally thicker or stiffer. Fiber composition, density, coating and manufacturing affect those properties.

What lb paper weight measures

In the U.S. basis-weight system, a pound rating refers to the weight of a ream at the uncut basis size assigned to that grade of paper. The complication is that different grades use different basis dimensions. A pound of feathers has finally found a worthy rival: 80 lb paper may describe substantially different sheets depending on the category printed beside the number.

Text paper and cover paper are the most important distinction for many commercial jobs. Text stock is commonly used for book interiors, brochures and similar flexible pages. Cover stock is made for applications needing more body, such as covers, cards and inserts. Because their basis sizes differ, equal pound ratings do not indicate equal sheet mass.

Manufacturer examples illustrate the size of the difference: particular 80 lb text products are listed at approximately 118 GSM, while particular 80 lb cover products are listed at approximately 216 GSM. Their listed calipers also differ. These figures are product-specific examples, not universal conversion constants for every mill or paper line.

For a deeper explanation of why the categories cannot be compared by the number alone, see text weight versus cover weight paper.

GSM, lb, caliper and stiffness are different specifications

Specification	What it describes	What it does not establish
GSM	Mass per square meter	Exact thickness, stiffness or surface
Lb basis weight	Ream weight at a grade-specific basis size	A universal mass without the paper category
Caliper or points	Physical sheet thickness	Mass, bending resistance or printer compatibility
Stiffness	Resistance to bending under defined test conditions	Surface, coating or exact sheet weight

Caliper measures thickness. In common commercial-print terminology, one point equals 0.001 inch, so a nominal 10 pt sheet is 0.010 inch thick. A points label is therefore not another way of expressing GSM; it answers a different question.

Stiffness is different again. It describes resistance to bending, and standardized tests measure it separately from grammage and caliper. Two papers with similar GSM can bend differently because of their fibers, construction, density, grain and moisture condition. The practical lesson is simple: compare weight to understand mass, caliper to understand thickness and stiffness data or samples to understand bending behavior. Our guide to paper caliper versus paper weight examines that distinction in more detail.

Why generic lb-to-GSM charts can mislead

Use this comparison sequence instead:

Identify the paper category attached to the lb value, such as 80 lb text or 80 lb cover.
Find the manufacturer’s GSM value on the product datasheet or sample specification.
Check caliper separately if thickness affects feeding, folding, binding or the finished feel.
Compare surface, grain direction and stiffness when those properties affect the job.
Confirm compatibility with the exact printer, tray, duplex path and finishing equipment.

An online conversion can still be useful as an estimate when it explicitly uses the correct basis size. It should not replace the datasheet when a printer limit, folding requirement or finished thickness is at stake.

Surface can matter as much as weight

A GSM or pound value does not reveal whether the stock is coated, uncoated, glossy, matte or designed for a particular imaging process. Commercial paper catalogs treat surface and weight as separate choices. Coated stocks can produce a different color and reflectivity result, while uncoated stocks are generally easier to write on but may render color differently.

That distinction matters for postcards, reply cards and stationery. A heavy coated card may look polished but be awkward for handwriting unless its writability is verified. A lighter uncoated sheet may accept a pen more readily while feeling less rigid. If the project involves printed invitations and coordinating stationery, request the actual stock name, GSM or basis weight, caliper, finish and writability rather than relying on “premium cardstock” as a complete specification.

See coated versus uncoated paper for a closer look at appearance, handling and writing performance.

Folding introduces grain, caliper and coating

Heavier paper is not automatically unsuitable for folding, but it usually needs more deliberate production planning. Fold cracking can be affected by coating, stock weight, fold direction, scoring, production conditions and the surrounding environment. Sappi’s technical guidance on fold endurance identifies these as interacting variables rather than treating weight as the sole cause.

Grain direction is especially important. Paper generally folds more readily parallel to its grain, while folding across the grain can increase resistance and make surface cracking more apparent. For heavier stocks, a score or crease creates a controlled line before folding. Neenah’s guidance for one heavyweight folding-board product recommends channel scoring parallel to grain, while Sappi’s creasing recommendations use actual sheet thickness when selecting crease dimensions.

Dark ink coverage across a fold can make cracking more visible, particularly on coated stock. If a job includes folded cardstock, provide the printer with the exact stock and fold layout and ask how it will be scored. The distinction between scoring and creasing cardstock matters more here than another approximate weight conversion.

Printer compatibility requires the exact model and path

A printer advertised as accepting cardstock does not necessarily accept every sheet described as cardstock. Supported media can vary by model, tray, media type, weight, caliper and whether automatic duplexing is used. Manufacturer documentation should take priority over a generic recommendation.

For example, one HP LaserJet specification supports 105–163 g/m² cardstock through its multipurpose tray while excluding several listed heavy media categories from automatic duplexing. That is a model-specific limit, not a rule for laser printers as a class. Canon support documentation likewise shows why compatibility needs to be checked against the exact machine rather than inferred from the word “cardstock.”

When evaluating a desktop printer, consult its manual or the manufacturer’s current media table. HP’s paper-media overview also explains that weight, size, finish and printer technology all belong in the selection decision. Check the maximum supported weight and caliper, approved media types, required tray, feed orientation and duplex restrictions. A stock that feeds once through a straight manual path may still be unsuitable for automatic two-sided printing.

Paper weight does not change image resolution requirements

GSM, lb and caliper describe the physical sheet. They are not image-resolution units, so moving from 80 lb text to 100 lb cover does not by itself create a new PPI or printer-DPI requirement. File preparation changes only where the job specification changes.

A heavier or differently finished stock may still affect production decisions. Confirm the trim size, bleed, safe area, printing sides, fold and score positions, grain requirements and finishing tolerances. If the stock has a visibly different surface or color, request an appropriate proof because the same artwork can reproduce differently on another substrate. Duplex cards also require attention to front-to-back alignment and opacity, neither of which is guaranteed by the weight label alone.

A practical paper-weight checklist

Before approving a cardstock or paper choice, record the complete specification:

GSM and, when supplied, the full basis-weight label such as 80 lb text or 100 lb cover
Caliper in points, mils, inches or millimeters
Coated or uncoated surface and the named finish
Grain direction for folds or other directional finishing
Stiffness or a physical sample when rigidity affects the product
Printer model, tray, media setting and duplex restrictions
Score, crease, fold, trim, binding or mailing requirements
Writability, opacity and color expectations relevant to the finished piece

For a quick cross-market comparison, GSM is usually the clearest starting point. For purchasing and production, the full answer is the product datasheet plus the printer or provider specification. Treat lb as incomplete unless its category is stated, and never use weight as a substitute for caliper, stiffness or surface. Paper has several specifications because it has several ways to cause trouble.