Understanding Paper Weight & Thickness: GSM vs. PT Guide for Packaging

Key Facts for Packaging Buyers

• GSM means weight: grams per square meter, commonly used in China, Europe and many Asian packaging supply chains.
• PT means thickness: point, or thousandths of an inch, commonly used by many North American packaging buyers.
• Conversion is approximate: 350gsm does not always equal the same PT across every paper grade because density and material structure vary.
• Folding carton range: 300–400gsm is common for many retail folding cartons, depending on size, product weight and structure.
• Rigid box specification: rigid setup boxes are usually specified by greyboard thickness, such as 1.5mm, 2mm or higher.
• Important risk: thicker paperboard may improve stiffness, but it can also increase cracking, folding difficulty and production cost.
• Best practice: approve a physical sample before mass production when product fit, paper stiffness, folding lines or premium feel are important.

Why Paper Weight Matters in Custom Packaging

Paper weight affects how a custom box feels, folds, protects the product and performs during production. A board that is too thin may feel weak. A board that is too thick may crack on fold lines or become difficult to glue.

The best paper thickness is not the highest number. It is the material that fits your product weight, box size, printing method, finish, packing process and shipping conditions.

HS PACKFACTORY was founded in 1999 in Shenzhen, China. As a family-owned custom packaging manufacturer, we help overseas B2B buyers compare paperboard, greyboard, corrugated board, finishes and samples before mass production.

1. What Is GSM in Packaging Paper?

GSM stands for grams per square meter. It measures the weight of a paper sheet based on one square meter of material.

In China, Europe and many Asian packaging supply chains, paper mills and packaging factories often quote paperboard by GSM. This is common for custom folding cartons, paper bags, sleeves, inserts and many printed paper packaging projects.

Higher GSM often means a heavier and stiffer board, but it does not always mean the same actual thickness across different paper grades. A dense 300gsm board can feel different from another 300gsm board if the fiber structure, coating or surface treatment is different.

Common GSM examples

• 250gsm may be used for lightweight inserts, sleeves or small paper packaging components.
• 300gsm may work for small folding cartons and lighter retail products.
• 350gsm is commonly used for many standard retail folding cartons.
• 400gsm may be considered for heavier folding cartons or products that need more stiffness.

2. What Is PT or Caliper?

PT stands for point. It is an imperial unit used to describe paper thickness. One point equals 0.001 inch.

For example, 18pt paperboard is about 0.018 inch thick. Many buyers in the United States and Canada use PT because it describes the physical thickness they can feel with a caliper.

PT is useful, but buyers should still confirm the material grade. Two boards with similar thickness can feel different if they have different density, coating, fiber structure or stiffness.

How to measure PT

• Use a digital caliper or micrometer.
• Measure a single, unglued flap of the box.
• Do not measure glued seams or folded double layers.
• Measure several points if the paper surface is textured or laminated.

3. GSM vs PT Conversion Chart for Packaging Buyers

GSM-to-PT conversion is always approximate. The final thickness depends on paper grade, fiber density, coating, lamination and supplier specification.

The chart below is a practical reference for B2B packaging discussions. Buyers should confirm final caliper through material samples or physical packaging samples.

4. Which Paper Thickness Should You Choose?

The right paper thickness depends on the product and the box structure. A small lipstick carton and a large candle jar box should not use the same specification only because both are retail boxes.

For standard retail folding cartons

Many standard retail folding cartons use 300–400gsm paperboard. For cosmetics, skincare, supplements and light consumer products, 350gsm is often a practical starting point.

However, the final choice should be confirmed by product weight, carton size, locking structure, printing, coating and sample testing. For a broader planning view, buyers can also review our Custom Product Boxes Guide.

For heavier products

Heavier products may need thicker paperboard, reinforced structure or corrugated board. If the product is a glass jar, electronics item, candle or heavy bottle, paperboard thickness alone may not provide enough protection.

In these cases, review custom corrugated boxes or add a custom box insert to improve protection and product fit. If shipping cost is a concern, the structure should also be reviewed for carton size and volumetric weight, as shown in our structural mailer redesign case study.

For rigid setup boxes

Rigid setup boxes are usually made with greyboard or chipboard wrapped with printed paper or specialty paper. Buyers should specify greyboard thickness, such as 1.5mm, 2mm or higher, depending on box size and product value.

For premium structures, review our custom rigid setup boxes and compare them with folding cartons in our Rigid Boxes vs Folding Cartons Guide.

5. C1S vs C2S Paperboard: What Is the Difference?

C1S means coated one side. One side has a smoother coated surface for printing, while the other side is usually less coated or uncoated.

C2S means coated two sides. Both sides are coated for smoother printing or a more finished appearance.

For many folding carton projects, C1S paperboard is common because the outside prints well and the inside can support gluing or product-side requirements depending on the structure. C2S may be considered when both inside and outside surfaces need a more finished printed look.

Buyer decision points

• Does the inside of the box need printing?
• Will the inside surface touch the product directly?
• Does the structure need strong glue performance?
• Does the brand require a premium inside appearance?
• Will the coating affect food-contact, recyclability or other requirements?

6. Why Thicker Paperboard Can Crack on Fold Lines

Thicker paperboard can feel stronger, but it can also become harder to fold. If the crease line is not designed correctly, the paper surface may crack after folding.

Cracking risk increases with thick board, dark ink coverage, matte lamination, soft-touch surfaces, coated papers and tight fold angles. This is why buyers should not assume that a thicker board is always stronger or safer. For paper bag projects, the same idea is explained in our guide: Are Thicker Paper Bags Always Stronger?

How to reduce fold cracking risk

• Use proper creasing lines based on paper thickness.
• Avoid using overly thick board for small tight-fold cartons.
• Test dark-color artwork on the actual paper surface.
• Use samples to confirm fold performance before bulk production.
• Review finish choices such as matte lamination, soft-touch or heavy coating.

For finish-related planning, review our Packaging Finishes Guide. If color accuracy matters, also compare CMYK vs Pantone for packaging color control before approving artwork.

7. Paper Weight by Packaging Application

Different packaging applications need different paperboard choices. The table below gives general guidance for early sourcing discussions.

Buyer Checklist Before Sampling

Before requesting a sample or quotation, prepare the details below so the packaging factory can review the correct material direction, structure and quality risks.

Quality Control for Paper Thickness and Box Structure

Paper thickness should be checked during sample approval and production inspection. A material that looks similar on screen may feel different in hand.

Before mass production, buyers should confirm the material sample, physical box sample, folding performance, glue strength, print result and carton packing method.

• Measure a single unglued flap with a digital caliper.
• Check folding lines for cracking, whitening or surface damage.
• Test product fit, box closure, insert layout and stacking performance.
• Compare sample stiffness with the approved material specification.
• Keep the approved sample as a production reference.

If your packaging needs labels, barcodes or serialized tracking, confirm label material and adhesive together with the box structure. You can also review our Barcode & Serial Labels page.

Why Work With HS PACKFACTORY?

Paper weight decisions affect structure, cost, printing, production stability and customer experience. HS PACKFACTORY helps buyers review these risks before sampling and mass production.

• Founded in 1999: long-term experience in custom paper packaging manufacturing for overseas B2B buyers.
• Family-owned factory: stable communication, practical engineering support and factory-direct pricing.
• Located in Shenzhen, China: convenient access to paperboard, greyboard, corrugated board, printing, finishing and export logistics.
• Free dieline support: our packaging engineers can review product size, paper thickness, fold lines and box structure before sampling.
• Fast sampling: samples usually take 3–5 days for many custom packaging projects, depending on structure, material, printing and finish requirements.
• Complete packaging support: folding cartons, rigid boxes, corrugated boxes, paper bags, inserts, labels, manuals and display boxes.