Kraft Paper Grammage (GSM): Concept, Meaning and How to Choose

Reviewed and updated by ICD - Week 44/2026

Kraft paper grammage is the mass of one square metre of paper, in g/m² (gsm), measured according to ISO 536. Common Kraft paper has a grammage of about 40 to 135 g/m², while multi-ply Kraft board for boxes can run from about 195 to 415 g/m². Grammage decides most of the thickness, stiffness, load capacity and even the price of Kraft paper, so choosing the right grammage both protects the goods and avoids waste.

I am Le Van Thang, and I have worked at ICD Vietnam since 2011. When a customer sends a paper or packaging data sheet, the question I ask back is: by which standard was this figure measured, and what is the tolerance? This article explains grammage from how it is measured, how to read the tolerance and how to convert US units, to how to choose the grammage for container cargo.

1. What is Kraft paper grammage?

Grammage is the mass of paper per unit area, and the international unit is g/m². If Kraft paper has a grammage of 80 g/m², a sheet 1 m wide and 1 m long weighs 80 grams; at 300 g/m² a square metre weighs 300 grams, much thicker and heavier. To picture it, ordinary office paper is 80 g/m², so one A4 sheet weighs about 5 grams.

Grammage is not only weight. It is tied directly to the three properties that make up the strength of packaging. A higher grammage usually gives thicker paper with better puncture resistance. Heavier paper is also stiffer and deforms less under pressure, so a box keeps its shape better. And heavier paper usually resists tension, compression and tearing better, which are important figures for load-bearing uses.

2. Common Kraft paper grammage groups and their uses

Kraft paper has a wide grammage range, serving everything from consumer packaging to industry. The milestones below use only figures with a published source; each mill has its own grammage catalogue, so when ordering, ask for your supplier’s own catalogue.

2.1. Low-grammage Kraft paper

This group is thin, flexible, elastic and low in cost. It is used for light food paper bags, single-use bags, gift wrap, scratch-protection lining paper and paper packaging that needs to bend. The outermost layer of a dunnage bag also belongs to the thin group: the ICD Vietnam construction diagram states that this layer is 65 gram laminated Kraft paper. It is also the material behind the Kraft paper dunnage bag; the strength of the bag comes from both the laminated shell construction and the plastic air-holding liner, not from the sheet of paper alone.

2.2. Medium-grammage Kraft paper

This group is moderately stiff, balancing strength and cost, and is widely used for ordinary Kraft paper bags, medium-load shopping bags and the facing (liner) of corrugated cartons. In the United States liner is usually named by pounds per 1,000 ft²; for example 42 lb liner is about 205 g/m² by the conversion in section 4.

2.3. High-grammage Kraft paper and board

High-grammage paper and board is thick, very stiff, and good at resisting compression and puncture. It is used for load-bearing cartons (3-ply, 5-ply), boxes for heavy products such as electronics, machinery and bottles, and as liner for industrial cartons that need high compression strength. For example, the Stora Enso CKB multi-ply Kraft board range runs from about 195 to 415 g/m².

2.4. Heavy board and heavy industrial uses

For heavy-load industrial uses, people usually do not use one very thick sheet but laminate several layers. Cement, flour and fertiliser sacks are multi-wall sacks made from thin, tough sack kraft with stretch to survive drops. A 5-ply corrugated carton (A and C flutes combined) reaches high compression strength through the flute structure and the liner, not only the grammage of a single layer. Jumbo bags (FIBC bags) alone are made of woven PP fabric, not Kraft paper.

3. Choosing the best Kraft paper grammage

The best grammage is the level that just protects the goods in your specific transport chain at the lowest cost. Four factors need to be weighed: the load and size of the goods, the transport conditions and humidity, printing requirements, and the packaging production machines.

3.1. Product weight, size and compression strength

This is the most important factor: the heavier the goods and the bigger the carton, the more load and stacking weight the box shell must carry, and the more grammage or construction the paper needs. For cartons, the figure commonly used is box compression strength (BCT, Box Compression Test). If the liner is too thin, the carton easily dents and collapses when stacked in a warehouse or container.

BCT does not rise linearly with grammage. The simplified McKee formula presented by Georgia Tech estimates BCT = 5.87 × ECT × √(Z × t), where ECT is the edge crush strength of the board, Z is the carton perimeter and t is the board thickness. Raising liner grammage raises ECT and thickness, and so BCT rises, but the increase depends on both the flute type and the carton size, so it needs to be calculated or tested rather than added proportionally.

3.2. Mode of transport and moisture risk

Goods that travel a long way, are handled many times or are stored in damp conditions need stronger, stiffer paper. Kraft paper absorbs moisture, and its strength drops clearly as humidity rises: a Clemson University study of 3,000 cartons records that each extra 1% of moisture cuts compression strength by about 7%. So for sea or export cargo, choose a grammage or construction above the minimum that would be enough in a dry warehouse.

Another solution is to use PE-laminated Kraft paper to create a water vapour barrier. The lamination does not raise the strength of the base paper, but keeps the paper drier, so it holds its inherent load capacity in a damp environment.

3.3. Printing and appearance requirements

Grammage also affects print quality and brand perception. With flexo printing, the common technique on cartons, thicker paper is usually flatter and less wavy, so the print is sharper, while paper that is too thin wrinkles or tears easily on the press. Some brands deliberately choose paper thicker than a light product needs, so the bag feels solid in the hand and gives a premium, durable impression.

3.4. Production process considerations

The grammage must suit the machines. Paper that is too thick can trouble folding, cutting or corrugating machines, slowing the line and raising the defect rate. When changing to a new grammage, run a small trial batch on the very machine that will make the product.

4. Standards and grammage control for Kraft paper

Grammage control is part of quality management, because deviations in grammage directly affect cost and the safety of the packaging. Three things need to be known: how to measure, what tolerance is normal, and how to convert when the data sheet uses US units.

4.1. Test standards (ISO and TAPPI)

The ISO 536 standard specifies how to determine the grammage of paper and board: cut a sample of exact area with a knife or die with an error of no more than ±1.0% of the nominal area, then weigh it. The usual sample area is 50,000 to 100,000 mm², that is 500 to 1,000 cm²; using a sample outside this range must be stated in the report. The sample is conditioned in test-room conditions according to ISO 187 (23°C, 50% humidity) before weighing, and the result is recorded to three significant figures. In the United States the equivalent method is TAPPI T 410.

On tolerance, there is no single figure for every kind of paper; each mill publishes a tolerance for each product line. For example, Stora Enso publishes a grammage tolerance of ±4% for its CKB Kraft board range, measured to ISO 536. When goods arrive, compare the measured grammage with the tolerance in that supplier’s own data sheet: below the tolerance the packaging may not carry the load, and far above it you are paying for extra paper.

4.2. Converting grammage to US units

US makers often state “basis weight” in pounds per ream of a standard area, instead of g/m². Paper uses an area of 3,000 ft², while board and liner use 1,000 ft². ICD Vietnam converted from the unit definitions (1 lb = 453.6 g; 1 ft² = 0.0929 m²) as follows:

4.3. Paper grammage and packaging production cost

Grammage is proportional to the mass of paper used, so the higher the grammage, the higher the material cost. For example, a 120 g/m² paper roll 1,000 m long and 1.2 m wide has an area of 1,200 m² and weighs about 144 kg; the same roll at 80 g/m² weighs only about 96 kg.

Conversely, cutting grammage too far to save money can lead to damaged goods, causing far greater loss than the initial saving: rework, re-shipping, insurance and reputation with the buyer. That is why packaging makers always look for the optimal grammage, just enough to protect the product without waste.

5. Frequently asked questions about Kraft paper grammage

What is Kraft paper grammage?

It is the mass of paper per square metre, measured in g/m² (grams per square metre) according to ISO 536. For example, 80 g/m² paper means one square metre of paper weighs 80 grams.

What is the usual range of Kraft paper grammage?

Common Kraft paper has a grammage of about 40 to 135 g/m² according to Wikipedia, while multi-ply Kraft board for boxes is heavier, for example the Stora Enso CKB range from about 195 to 415 g/m². Each mill has its own grammage catalogue.

What does grammage affect?

Grammage directly affects thickness, stiffness, load capacity (tension, compression, tearing, puncture resistance) and the price of Kraft paper. Even so, fibre type and production method also decide strength, so the same grammage does not always mean the same load capacity.

Is a higher Kraft paper grammage always better for cartons?

Not entirely. A high grammage raises the carton’s compression strength so the box carries load better, but going higher than needed wastes cost. The best grammage is just enough to carry the stacking load and protect the goods in your specific transport chain.

Does Kraft paper grammage affect recyclability?

Not significantly. Heavier paper simply means more fibre to re-pulp. Unbleached, uncoated Kraft paper is easy to recycle regardless of grammage; what makes recycling harder is the PE coating or plastic film lamination.

Can 150 g/m² Kraft paper be used to make a dunnage bag?

A single sheet of paper, however thick, cannot make an air bag, because the bag needs a plastic air-holding liner and a laminated, moisture-resistant shell. The ICD Vietnam construction diagram states that the outermost layer is 65 gram laminated Kraft paper, and the catalogue places the Kraft bag at Level 1, withstanding a compression force of up to 15,000 lbs. The strength comes from the whole bag construction, not from the paper grammage alone.

How does paper weight differ from paper grammage?

Grammage is a property of the material, in g/m², fixed for a given paper. Weight is the actual total mass of a roll or bundle of paper, in kg or tonnes, equal to grammage times area. For example a 120 g/m² roll with an area of 1,200 m² weighs about 144 kg.

6. Contact for technical advice

References

• The concept of Kraft paper grammage - TAPPI (Technical Association of the Pulp and Paper Industry); TAPPI T 410 method (grammage of paper and paperboard).
• ISO 536:2019 - Paper and board, determination of grammage (sample copy of the standard, linked in section 4.1).
• Stora Enso - CKB PE, technical data sheet: grammage, ±4% tolerance to ISO 536.
• Georgia Tech - effect of moisture on carton compression strength: McKee formula, effect of humidity.
• Clemson University - study of the effect of moisture on carton compression strength (2019).
• Wikipedia - Kraft paper, Grammage and Flexography: grammage ranges, basis weight, flexo printing.
• ICD Vietnam construction diagram and dunnage bag catalogue: 65 gram laminated Kraft paper layer, levels and compression force.