What GSM means · one number that describes the weight of paper
GSM stands for Grams per Square Metre. It is the weight of one square metre of paper or board, measured in grams. A single sheet of A4 paper cut to exactly one square metre would weigh the GSM value of that paper. It is the universal standard for expressing paper weight and is used by every paper mill, printer, and print buyer in India and globally.
GSM is a weight measurement, not a thickness measurement. Two papers with the same GSM can have different thicknesses (caliper). A 130 GSM gloss coated art paper is noticeably thinner than a 130 GSM uncoated offset paper of the same weight, because the coating on the art paper is denser and more compact than the looser, more open fibre structure of uncoated paper. This distinction between weight and thickness is one of the most common sources of confusion in print specifications.
Standard A4 office copy paper is 80 GSM. A business card is typically 300–350 GSM. A cereal box is typically 300–400 GSM board. If something feels like paper, it is probably below 200 GSM. If it feels like card or board, it is probably above 200 GSM. Everything else is a matter of degree between these reference points.
How GSM is measured · the standard method
GSM is measured to ISO 536, the international standard for paper grammage. The method is simple: cut a sample of paper to a known area (either exactly 1 square metre, or a smaller sample whose area is precisely calculated), weigh it on a calibrated analytical balance, and express the result in grams per square metre.
The standard test method
- Condition the paper to standard atmosphere: 23°C ± 1°C and 50% ± 2% relative humidity for minimum 4 hours before measurement
- Cut a minimum of 5 samples from different positions across the sheet (edges and centre) using a precision die cutter or guillotine. Sample size: 100cm² (10cm × 10cm) is the most common for laboratory use
- Weigh each sample on an analytical balance accurate to 0.001g
- Calculate: GSM = (mass in grams × 10,000) ÷ sample area in cm²
- Average the five readings. Report the result to the nearest 1 GSM.
Practical mill certificate values
Every reel or ream of paper from a reputable mill comes with a mill certificate (also called a test report or certificate of analysis) that states the measured GSM of that production lot. The measured GSM will typically be within ±5% of the nominal (specification) value, a ream labelled 130 GSM may contain paper measuring 124–136 GSM, all within acceptable tolerance.
For jobs where paper weight affects a measurable outcome, spine width calculations for a bound book, carton gluing performance, regulatory weight declarations on packaging, always request the mill certificate and verify the actual GSM before committing to the specification. The nominal value on the wrapper and the actual measured value can differ by up to 5%. On a 200-page book, a 5% GSM variation changes the spine width by 0.5–1mm, enough to misalign spine text.
GSM vs caliper · weight and thickness are not the same thing
Caliper is the physical thickness of the paper, measured in microns (µm) or millimetres with a micrometer. GSM is the weight. They are related, heavier paper tends to be thicker, but the relationship is not fixed. It varies with paper type, coating, density, and manufacturing process.
| Paper type | Nominal GSM | Typical caliper (µm) | Bulk factor (µm/GSM) | Why bulk differs |
|---|---|---|---|---|
| Gloss coated art | 130 GSM | 100–115 µm | 0.77–0.88 | Dense coating compresses the sheet, thin for its weight |
| Matte coated art | 130 GSM | 110–125 µm | 0.85–0.96 | Matte coating slightly less compressed than gloss |
| Uncoated offset | 130 GSM | 140–160 µm | 1.08–1.23 | Open fibre structure, thicker for same weight than coated |
| SBS board | 300 GSM | 380–420 µm | 1.27–1.40 | Multi-ply structure, significant bulk |
| FBB board | 300 GSM | 420–470 µm | 1.40–1.57 | Mechanical pulp core, higher bulk than SBS at same weight |
| Duplex board | 300 GSM | 430–480 µm | 1.43–1.60 | Grey back multi-ply, high bulk, lower stiffness than SBS |
Why this distinction matters in practice
- Spine width calculation, spine width is calculated from caliper, not GSM. A book with 200 pages of 130 GSM gloss art (caliper 0.11mm) has a very different spine width than a book with 200 pages of 130 GSM uncoated offset (caliper 0.15mm). Get caliper from the mill certificate, not from GSM
- Carton stiffness, a carton's resistance to bending is determined by caliper (specifically the cube of the caliper), not by weight. FBB board at 300 GSM has a significantly higher caliper than SBS at 300 GSM and therefore greater stiffness, even at the same weight
- Crease and die-cutting specification, die-cutting crease channel width is specified by caliper, not GSM. A die made for 300 GSM SBS will not perform correctly on 300 GSM FBB because the caliper is different
- Transport and packing calculations, weight is relevant here, so GSM applies. But the physical volume of a ream depends on caliper, not GSM
For commercial print, specifying by GSM is usually sufficient. For packaging, it is not. A packaging specification that says "300 GSM SBS" is complete. One that says "300 GSM" without specifying the board grade is not, because 300 GSM FBB, SBS, and duplex have significantly different caliper, stiffness, printability, and cost. Always specify both GSM and board grade for packaging. The caliper should also be specified or confirmed from the mill certificate.
The complete GSM reference table · 60 GSM to 450 GSM
This is the reference table that answers the question "which GSM should I use?" for every common printing application. It covers commercial print, packaging, stationery, and books. Use it as a starting point, specific print buyers, brand guidelines, and technical constraints may call for adjustments.
| GSM range | Common paper types | Typical applications | Feel and characteristics |
|---|---|---|---|
| 55–65 GSM | Newsprint, thin offset | Newspapers, mass-market inserts, low-cost flyers | Very lightweight, translucent when held to light, significant show-through |
| 70–80 GSM | Standard copier paper, thin offset | Office documents, bulk photocopying, internal handouts, economy booklet text | Standard office paper feel. 80 GSM is the most common office paper in India. |
| 90–100 GSM | Quality uncoated, light coated | Letterheads, quality forms, economy brochure text, text pages in corporate documents | Noticeably more substantial than 80 GSM. Letterhead standard in India. |
| 115–130 GSM | Coated art (gloss or matte), premium uncoated | Brochure and catalogue text pages, flyers, quality leaflets, magazine pages | The standard for commercial brochure printing in India. Crisp, smooth, good colour reproduction. |
| 150–170 GSM | Coated art, premium uncoated | Brochure covers (saddle-stitched), flyer cards, premium leaflets, quality calendars | Noticeably heavier than brochure text. Feels like a proper cover stock. |
| 200–250 GSM | Coated or uncoated cover board, light card | Brochure and catalogue covers (perfect bound), postcards, greeting cards, premium flyers | Clearly card-weight. Does not curl easily. Standard for most brochure covers. |
| 270–300 GSM | Cover board, business card stock, light SBS | Business cards, high-quality invitation cards, book covers, presentation folder covers | Business card weight range. Stiff, premium feel. Will not bend easily under normal handling. |
| 300–350 GSM | SBS board, FBB board, coated board | Folding cartons (standard to premium), retail packaging, pharma cartons, cosmetics packaging | The standard weight range for most Indian mono carton packaging. Stiff enough to erect and hold shape. |
| 350–400 GSM | SBS board, FBB board | Premium retail cartons, luxury cosmetics packaging, high-end confectionery, spirits packaging | Noticeably heavier and stiffer than standard carton board. Communicates premium quality by weight alone. |
| 400–450 GSM | Heavy SBS, heavy FBB, duplex board | Rigid gift boxes (lid and base), heavy-duty retail bags, specialist packaging | Very stiff board. Approaching the limit of what can be folded without scoring. Rarely used for folding cartons. |
| 600–2000+ GSM | Greyboard, chipboard, rigidboard | Rigid box (clamshell, drawer, shoulder) bases and lids, case binding boards, display stands | Cannot be folded, used for rigid structures. The board for premium rigid gift boxes. |
GSM for commercial print · the decisions that matter most
GSM for packaging · board weight and board grade together
In packaging, GSM is necessary but not sufficient. The board grade, SBS, FBB, duplex, greyboard, determines how the board performs structurally and in printing. Two boards at the same GSM but different grades behave differently in die-cutting, creasing, printing, and finishing. Always specify both.
| Packaging application | Typical GSM range | Board grade | Key selection reason |
|---|---|---|---|
| Pharma, tablet / capsule mono carton | 240–300 GSM | SBS (Solid Bleached Sulphate) | Food-adjacent regulatory compliance, clean white top, hygienic surface, SBS is the pharma standard in India |
| FMCG folding carton, standard | 300–350 GSM | SBS or FBB | Must hold shape through distribution. SBS for better printability; FBB for lower cost at equivalent caliper. |
| Premium cosmetics carton | 350–400 GSM | SBS | Weight communicates premium. SBS surface handles lamination, foil, and emboss better than FBB at this weight. |
| Food, confectionery, biscuit carton | 300–380 GSM | SBS or FBB | Food safety compliance required. SBS preferred for primary food-adjacent applications. FBB acceptable for secondary packaging. |
| Spirits, premium liquor carton | 380–450 GSM | SBS | Maximum stiffness and heft. Premium presentation. SBS at heavy weight handles deep emboss and combination foil. |
| Economy packaging, secondary | 250–300 GSM | Duplex or FBB | Cost-driven. Duplex uses recycled grey back for economy. Not suitable for food-contact applications. |
| Rigid gift box, lid and base | 1200–2000 GSM | Greyboard (chipboard) | Cannot fold, rigid structure. Wrapped with printed paper. The greyboard provides the structural form. |
For commercial print, specifying GSM and paper type (coated or uncoated, gloss or matte) is generally sufficient. The press and paper supplier will handle the rest. Where specific brands are required (for colour matching, print quality, or client specification), name the brand alongside the GSM.
For packaging, the complete specification is: GSM + board grade + caliper + coating (single-side or double-side coated) + any regulatory requirements (food-safe, migration-compliant). A packaging specification that lacks any of these elements is incomplete and leaves room for a supplier to substitute an inferior or non-compliant material.
How to choose the right GSM · the decision framework
Choosing the right GSM involves balancing four factors: the functional requirement of the piece, the aesthetic and tactile quality intended, the budget, and any technical constraints (binding method, printing process, lamination compatibility).
Step 1 · What does the piece need to do physically?
- Does it need to stand upright? (menus, table cards, display cards), minimum 300 GSM for self-standing
- Does it need to fold repeatedly? (leaflets, concertina folds), keep below 250 GSM for clean folding without scoring. Above 200 GSM should be scored before folding.
- Does it need to go through a laser printer after offset printing? (letterheads), maximum 120 GSM for reliable laser printer feed
- Does it need to be saddle-stitched? (booklets), cover should not be more than 3–4× the text weight to avoid spine swell problems
- Does it need to erect into a carton shape? (packaging), minimum 250 GSM for any self-erecting carton
Step 2 · What quality level is intended?
- Economy: use the minimum weight that meets the functional requirement. For a flyer: 115 GSM. For a brochure: 115/170 GSM text/cover. For a carton: 280 GSM duplex.
- Standard: one step up from economy. Brochure: 130/200 GSM. Carton: 300 GSM SBS.
- Premium: a noticeably heavier weight than standard. Brochure: 150/250 GSM. Business card: 350 GSM with lamination. Carton: 350–400 GSM SBS with emboss and foil.
Step 3 · What are the technical constraints?
- Binding method limits page count at certain weights, check saddle stitch limits in the Binding guide
- Creasing specification changes with GSM (and caliper), check the Die-Cutting guide
- Lamination performance varies with substrate weight, heavy board above 400 GSM needs wet lamination, not thermal
- Spine width for bound books depends on caliper, get the caliper from the mill certificate, not the nominal GSM
Common GSM mistakes · what goes wrong and how to avoid it
These are the GSM-related specification errors that cause problems most often in Indian commercial and packaging print, and how to prevent each one.
| Mistake | What happens | How to avoid it |
|---|---|---|
| Using 80 GSM for a brochure that needs to look premium | The brochure feels flimsy, shows ink show-through, and does not communicate the intended quality. The client is dissatisfied even though the printing is technically correct. | Brief the client on minimum weight for intended quality level. Standard brochure text: 115–130 GSM. Premium: 150 GSM. Never specify below 115 GSM for coated art commercial brochures. |
| Specifying cover and text on the same GSM for a saddle-stitched booklet | The booklet has no visual hierarchy, the cover does not feel different from the pages. The booklet looks and feels unprofessional even with good design and printing. | Cover should be minimum 1.5× the text weight: if text is 130 GSM, cover minimum 200 GSM. Standard: 130/250 GSM or 115/200 GSM text/cover. |
| Specifying packaging board by GSM only without specifying grade | Supplier substitutes duplex board at same GSM as specified SBS, dramatically different caliper, stiffness, and surface quality. Carton fails to erect correctly or looks inferior. | Always specify: GSM + grade + caliper. "300 GSM SBS, caliper minimum 380 µm, double-side coated." |
| Calculating spine width from GSM instead of caliper | The spine text is positioned incorrectly, printed on the front or back cover rather than on the spine panel after binding. | Always calculate spine width from measured caliper. Request mill certificate. Do not use GSM to estimate caliper for spine calculations. |
| Laminating 400+ GSM board on a thermal laminator | Lamination bond is weak, the thermal laminator cannot generate sufficient nip pressure for heavy board. Edge lifting occurs within days of production. | Above 350–400 GSM, specify wet (adhesive) lamination, not thermal. Verify with your lamination supplier what the maximum substrate weight is for their thermal machine. |
| Using 250 GSM for a self-standing table tent or menu card | The card does not hold its shape, it leans and eventually lies flat. The finished piece looks cheap despite quality printing. | Self-standing cards require minimum 300 GSM, preferably 350 GSM, for A4 or larger. For smaller sizes (A5 tent card), 270 GSM with lamination may be adequate. |