Paper Weights explained: The meaning of Paper Basis Weight

What is the Basis Weight of Paper?

You have likely heard paper referred to by various names, such as Bond, Text, Cover, Index and others. These names refer to different categories of paper. Within each category there are various weights of paper.

Having a choice of different weights from each category helps people choose a paper with the density and thickness they desire for a given print project.

In the United States, a paper's weight is commonly expressed in pounds. Since the word "pound" is frequently abbreviated as "LB" or "lb", paper is often referred to as 20LB, 80lb, etc.

The "#" sign is another popular way to designate pounds, so you will also see paper weights being specified as 20#, 80#, and so on.

Each category of paper has a fixed basic size, which represents the standard sheet size from which the weight of paper is figured. The basic size varies from category to category, but the Basis Weight of a given paper stock is always based on 500 sheets of the paper in its basic size.

For example, the basic size of Bond paper is 17" x 22". If 500 sheets of 17" x 22" Bond paper weigh a total of 20 pounds, then the paper is labeled as 20lb or 20#. If 500 sheets of 17" x 22" Bond paper weigh a total of 32 pounds, the paper is labeled as 32lb or 32#, and so on.

Similarly, the basic size of Cover paper is 20" x 26". If 500 sheets of 20" x 26" Cover paper weigh a total of 80 pounds, then the paper is labeled as 80lb or 80#. If 500 sheets of 20" x 26" Cover paper weigh a total of 100 pounds, then the paper is labeled as 100lb or 100#.

If you live in the US, you are probably familiar with paper sizes like 8.5" x 11", 8.5" x 14", and 17" x 11". These are common sizes of paper that have been trimmed down to make convenient and easy-to-handle bundles. It is important to note that these "cut sizes" do not represent a paper category's basic size. The basic sizes are much larger, as you can see in the list below...

The Basic Sizes of Common Paper Categories

• Bond Paper - 17" x 22"

• Book Paper - 25" x 38" (includes Offset and Text weight stocks)

• Cover Paper - 20" x 26"

• Index Paper - 25.5" x 30.5"

You will notice that the basic sheet sizes shown for these paper categories are all different. Because the basic paper sizes differ by category, this can make things a little confusing when first learning about paper stocks and the concepts of basis weight and basic size.

Papers within the same category share the same basic sheet size. So when comparing two or more papers within the same category, a higher weight will always translate to a thicker stock. For example, 28# Bond will be a thicker stock than 24# Bond.

However, we cannot compare the weights of papers from different categories and confidently state that one will always be heavier or lighter than the other. This is because the basic sheet sizes are different from category to category.

For example, one might be inclined to think that 50# Offset is thicker than 20# Bond, based on the weight of 50# being 2.5 times greater than 20#. However, these two stocks actually have the same nominal paper thicknesses of .004". This is because the 25" x 38" basic sheet size for Offset paper has about 2.5 times the area of the 17" x 22" basic sheet size for Bond Paper. In other words, the thicknesses of the two paper stocks are the same but the Offset is labeled as 50# and the Bond is labeled as 20# because the basic sheet size for Offset is about 2.5 times bigger than the basic sheet size for Bond. Hence, 500 basic sized sheets of the Offset weighs 2.5 times more than 500 basic sized sheets of the Bond.

Another example of a higher pound weight paper not being thicker than a lower pound weight paper is 110# Index vs 100# Cover. A sheet of 110# Index has a nominal thickness of .0085 to .009" whereas 100# Cover is actually thicker, measuring around .0095" to .011" in thickness. Before reading this article you might have reasoned that the 110# Index would be thicker than the 100# Cover, but now you know that isn't the case because the Index category has a larger basic sheet size than the Cover category.

Grams per Square Meter (GSM)

Another system for expressing the basis weight of paper is Grams per Square Meter. Commonly abbreviated as GSM or gsm, the Grams per Square Meter method doesn't rely on a basic paper size. It simply provides the weight, in grams, of one square meter of paper. The higher the GSM, the higher the weight of the paper.

Being metric based, the GSM system is not as heavily used in the US as it is in other parts of the world...at least not yet.

Providing a few examples for reference, basic 20# Bond paper and 50# Offset paper both have a weight of 75 gsm. Likewise, 80# Text weighs 120 gsm, 110# Index weighs 200 gsm, and 100# Cover weighs 270 gsm.

Heavier Papers are often described using "Points"

Though some heavier cover stocks and cardstocks are described using the weight in pounds or gsm, others are described using the measured thickness (caliper) of the paper. The unit of measure for the thickness of these heavier stocks is usually shown as "Points", where one point equals 1/1000ths of an inch or .001".

For example, 10pt cardstock equates to a thickness of .010". Likewise, a 12pt stock is .012" thick, a 14pt stock is .014", a 16pt stock is .016" and so on.

While we're on the topic of thick stocks, it is probably a good time to mention that digital printing presses cannot usually print on paper that is thicker than 14pt. Also, most web-fed offset presses have an upper thickness limit of 8pt stock. Fortunately, most sheet-fed offset presses can handle cardstock thicknesses up to 24pt.

If you ever have a printing question, Color Vision is just a phone call away!

Like many industries, the printing trade has its share of confusing terminology. Hopefully, we have helped to clarify the meaning of Basis Weight as it pertains to paper.

Understanding the relative difference between various paper weights is important because it affects the paper's durability and print quality. It also contributes to the overall feel and perception of the finished product.

Should you have any questions or want to discuss an upcoming print project, give Color Vision a call at 800-543-6299.

Or, if you have your project's specifications handy and would like a quote, simply fill out our Quote Request form and we will email a quote to you. As always, we look forward to assisting with your next print project!