Paper weight explained: GSM, lb, text and cover

Updated 2026-10-11

The Core Distinction: Area Weight vs. Stack Weight

When you select paper for a project, you will encounter two primary measurement systems: GSM (grams per square metre) and lb (pounds). Understanding the difference between gsm vs lb paper weight is essential for ensuring your printed product has the correct thickness and durability.

GSM is an absolute measurement of area weight defined by ISO 536. It tells you exactly how many grams one square metre of the paper weighs. Because it is metric, it is the global standard and remains constant regardless of the paper’s physical dimensions.

Lb (or “basis weight”) is a North American system that measures the weight of a full ream (500 sheets) of paper cut to a specific “base size.” This is where confusion arises: the base size depends on the paper’s intended use. A “100 lb” text paper is much lighter than a “100 lb” cover paper because they start from different base dimensions.

Base Sizes and Categories

To convert between these systems accurately, you must know the paper category. The US paper trade defines three main base sizes:

1. Text/Book: Base size is approximately 25 × 38 inches. Used for book pages, brochures, and letterhead.
2. Cover: Base size is approximately 20 × 26 inches. Used for business cards, folders, and book covers.
3. Bond/Writing: Base size is approximately 17 × 22 inches. Used for legal pads, invoices, and stationery.

Because the base sizes differ, the conversion factors vary. You cannot simply divide lb by a single number to get GSM; you must apply the specific factor for that paper type.

Conversion Table

The following table provides approximate conversions for common business card and document stocks. Note that these are averages; specific mill specifications may vary slightly.

For business cards, you typically see stocks in the 300–400 GSM range. In the US system, this corresponds to roughly 14–16 pt cover stock. If you see a spec listed as “16 pt cover,” it is equivalent to approximately 300 GSM.

Practical Application

When reading a spec sheet, look for the category label. If a printer lists “80 lb text,” they mean a standard writing paper. If they list “80 lb cover,” they mean a significantly thicker cardstock. Always confirm the category to avoid ordering paper that is too flimsy for a business card or too thick for a document.

FAQ

Is 300 GSM the same as 16 lb paper? Not exactly. 300 GSM is equivalent to approximately 16 pt cover stock. It is much thicker than 16 lb text stock, which is only about 108 GSM. Always check if the “lb” refers to text, cover, or bond.

Why do some papers list “pt” instead of “lb”? “Pt” (points) is another way to express thickness, where 1 point equals 1/1000th of an inch. In the US trade, “16 pt cover” is often used interchangeably with “16 lb cover,” though technically “lb” refers to the ream weight and “pt” to physical thickness. They correlate closely for standard stocks.

Can I use GSM to compare paper from different countries? Yes. GSM is the most reliable metric for international comparison because it is not tied to a specific base size. If you are working with a supplier in Europe or Asia, GSM is the preferred specification to ensure consistency.