Choosing material stock with the right thickness is important for packaging and shipping. The thickness or thinness of your packaging can affect its durability, protectiveness, and overall look.
GSM and PT are two unit systems that help measure paper quality. They tell you about the weight and thickness of paper. If you know the difference, you can pick the right paper for your products.
In this guide, I’ll explain GSM and PT systems in simple words. It will help you understand how they work, where to use them, and how to compare them.
What is GSM Unit?
GSM stands for Grams per Square Meter. It shows how much a sheet of paper weighs based on its size. This unit uses the metric system (grams and meters).
GSM tells you how heavy or light the paper is, not how thick it feels. So, a sheet with a high GSM will usually be heavier and stronger.
Some papers may feel thick but are still light. Others may look thin but weigh more. This is the reason GSM measures weight, not just thickness.
For example, corrugated cardboard may feel thick because of the flutes inside, but it may not have a high GSM.
In most cases:
- A higher GSM means thicker and heavier paper.
- Lower GSM paper is softer, thinner, and used for things like notebooks or flyers.
Common GSM examples:
- 80 GSM – thin paper for printers and copiers.
- 120 GSM – good for flyers or letters.
- 200 GSM – thicker paper for posters or catalogs.
- 300+ GSM – heavy paper used in product packaging.
High GSM paper is often durable and prints better. That’s why it’s used for packaging, postcards, and premium prints.
What is PT Unit?
PT stands for Point. It shows the thickness of packaging corrugated paper or any other packaging material. This system is mostly used in the United States and Canada.
Each point (PT) equals 1/1000 of an inch. So, a 10 PT paper is 0.010 inches thick.
The thickness is measured using a tool called a caliper. This helps check how thick the material is, layer by layer.
You will often see packaging materials listed by point values like:
- 8 PT
- 10 PT
- 14 PT
- 16 PT
A higher PT means the paper is thicker and stronger. Thicker materials are better for protection, structure, and premium looks.
Common PT Examples:
- 10 PT – used for postcards.
- 14 PT – common for business cards.
- 18 PT – strong and thick for covers.
- 24 PT – used for boxes and packaging.
PT helps you understand how solid or stiff the paper will feel in your hand. It’s a good way to measure the packaging stock’s strength and thickness.
Why is the GSM Unit System Important?
GSM helps when you want to know the paper’s weight. This is useful for many reasons:
- Helps with shipping: Lighter GSM paper reduces the total weight of your packaging, which can lower shipping costs.
- Good for printing: Some high GSM paper is too thick for regular home printers. Knowing the paper’s weight helps you pick the right one for your printer.
- Easy to compare: GSM gives a clear number to show how heavy the paper is, making it easier to match with your printing or packaging design needs.
In printing, GSM is often more helpful than thickness. It shows how much ink a sheet can take and how durable it will be.
What are the key differences between GSM and PT?
Knowing the difference between GSM and PT makes it easier to pick the right material for your project. Both units are important, but they measure different things.
1. What They Measure
- GSM measures the weight of paper.
- PT measures the thickness of paper.
2. Type of Unit
- GSM uses the metric system and is measured in grams.
- PT uses the imperial system and is measured in points (1 point = 1/1000 of an inch).
3. Where They Are Used
- GSM is common in printing projects like flyers, brochures, and books, especially for international use.
- PT is often used for business cards, rigid boxes, and product packaging.
4. Accuracy and Feel
- GSM can feel different based on the type of paper. For example, coated and uncoated paper with the same GSM may feel different.
- PT shows the exact thickness, which helps when you need strong or stiff materials.
What are the challenges in converting between GSM and PT?
You can’t always change GSM into PT or the other way around. That’s because:
- Different papers have different densities.
- Coated paper is thinner than uncoated paper with the same GSM.
- Two sheets can have the same GSM but feel very different.
For example:
- 300 GSM glossy paper might be 12 PT.
- 300 GSM kraft paper might be 16 PT.
The paper type affects both weight and thickness. This is why the same GSM can give different PT numbers.
Converting Between the GSM and PT Unit Systems
GSM and PT are not the same, but they are often compared. These units don’t convert directly. That’s because GSM looks at weight, and PT looks at how thick the material feels.
Some thick papers are light. Some thin papers are heavy.
Still, many printers and packaging sellers use conversion charts to give a rough idea of how GSM and PT are organized.
Sample GSM to PT Comparison:
| Thickness / Packaging Material | Weight |
| 13 PT Pulp Board | 200 GSM |
| 14 PT Uncoated | 270 GSM |
| 16 PT C2S (Coated on Two Sides) | 350 GSM |
| 18 PT C2S | 400 GSM |
| 24 PT Uncoated | 405 GSM |
| 24 PT C2S | 460 GSM |
| 40 PT Cotton Stock | 600 GSM |
These numbers can help when working with a printer or supplier. But they are not exact. Different materials have different densities and textures.
For example:
- A 17 PT uncoated board may weigh 350 GSM.
- But an 18 PT Kraft board could weigh only 315 GSM, even though it feels thicker.
When to use GSM?
GSM is the best choice when you need to measure by weight. Here’s when to use it:
- Printing flyers or brochures: GSM helps you find the right balance between print quality and cost.
- Shipping: Knowing the GSM tells you how heavy your paper will be in large amounts, which affects shipping costs.
- Design projects: GSM helps you choose paper that is either flexible or firm, depending on what your project needs.
Use GSM when:
- Working with international teams.
- Creating lightweight marketing materials.
- Choosing photo paper or card stock for printing.
When to use PT?
PT is useful when you care more about thickness than weight. Here’s when to use it:
- Packaging boxes: PT helps you check how rigid and strong the box will be.
- Business cards: A higher PT gives a sturdy feel, which creates a strong first impression.
- Postcards: PT ensures the card is thick enough to handle mailing without damage.
Use PT when:
- Creating custom product packaging.
- Choosing premium thick materials.
What are the pros and cons of each system?
GSM and PT have some benefits and limitations, which are as follows:
Pros and Cons of GSM
Here are some common pros and cons:
GSM Pros:
- Easy to compare weights.
- Used worldwide.
- Good for light printing.
GSM Cons:
- Doesn’t show exact thickness.
- It can be confusing if the paper type changes.
Pros and Cons of PT
PT has some benefits and limitations, which are as follows:
PT Pros:
- Measures thickness directly.
- Perfect for rigid packaging.
- Helps choose strong and sturdy materials.
PT Cons:
- It can be confusing when comparing different materials.
- Thickness may not show how heavy or strong the paper is.
Which One Should You Choose?
Here’s a simple way to decide:
- Choose GSM if you’re printing lightweight items like flyers, booklets, menus, or photos. It’s better for international projects, too.
- Choose PT if you’re working on rigid packaging, luxury boxes, or business cards. It gives you better control over thickness.
Always ask your supplier which unit system they use. This helps avoid mistakes.
Conclusion
GSM and PT are both helpful. They just measure different things. GSM tells you the paper’s weight. PT shows the paper’s thickness.
Knowing how each one works helps you choose better paper and packaging. It makes your printing smooth and your brand look great.
If you want more help, talk to your printer or packaging supplier. They can give samples, guide you on units, and help you avoid errors.
Use this guide to make smart choices. Whether you print flyers or design packaging, understanding GSM and PT will save time and money.
