The thickness of book cover is measured in PT (point), and text or thin papers are measures in LB (pound). For example, 100lb Gloss Text which is typically used for brochures, and 70lb Uncoated Text which is commonly used for letterheads.
This article will provide more insight PT, LB, as well as GSM, another widely used measurement of paper.
GSM (Grams per Square Meter)
GSM is an acronym that stands for grams per square meter. The calculation is simply that the weight of one square meter of the stock equals so many grams. Typically, printers will refer to the gsm when buyers are looking at the different quality levels of the paper. The higher the gsm number, the heavier and thicker the paper. Paper with gsm that is higher is often considered higher quality paper stocks due to it being more durable and thick, allowing images to pop on either side.
To help you determine which gsm is best suited for your print project, it is essential to know what certain gsm weights are typically used for.
35 gsm to 55 gsm: This type of paper is considered extremely thin and almost delicate. This is the type of gsm that is used to print items such as a newspaper.
90 gsm to 100 gsm: Paper at this weight will be similar to copy paper that you will most often find in your home or at a copy center. It is best used for simple copy jobs, or jobs with less ink coverage as heavy ink coverage might still show through at this weight.
120 gsm to 140 gsm: When you get to this weight of paper you will find posters have a lot more durability. It is thick enough and heavy enough to be used for full-color flyers and to be used on posters or other types of bulletins.
210 gsm to 300 gsm: When you notice premium flyers and brochures they will often be at this weight range. You have not quite hit card thickness as the piece is still bendable easily with your fingers, but you will notice more resistance when trying to bend. This weight of paper is also most common for items such as booklet and magazine covers.
350 gsm to 400 gsm: This level of thickness is often what people may refer to a card or cover stock and is marked by its ability to stand on its own weight. You will find this thickness of paper for everything from business cards to wedding invitations.
PT, or point, is a way to calculate the thickness of paper stock by using the caliper of the paper. Printers and paper manufacturers will measure the caliper of the paper using a micrometer. Paper caliper is determined in thousandths of an inch. This measurement is then calculated as a point, with one point being equal to one-thousandth of an inch or .001 inch. Therefore, a stock that is 10pt would measure .010 for its caliper.
This measurement is used for calculating the weight of paper for shipment, as well as the thickness to determine which machine the stock can be printed on. The higher the points, the thicker the paper. Digital machines can be rated for up to 18pt to 24pt stock, while conventional presses can run up to 40pt or even higher. Though the gsm and point thickness can vary depending on the type of stock as well as features such as finishes, you can use the below conversions as a basic rule of thumb when trying to compare the two.
3 to 6 pt. the paper will come in around 60 gsm to 120 gsm - Typical for copy papers and less durable flyers.
9 pt. to 14 pt. the paper will run between 199 gsm and 300 gsm - Used for posters and more durable marketing pieces.
14 pt.+ papers will usually start at about 310 gsm - Often used for the pointing of tags, header cards, and heavy covers.