Paper Weight Converter

Paper weight is one of the most confusing specifications in printing and stationery. A single sheet of paper may be described as "80 GSM," "20 lb Bond," "50 lb Text," or "65 lb Cover" — and all four of these descriptions can refer to a similar weight of paper depending on the system being used. Understanding how these systems work and how to convert between them is essential for graphic designers, printers, office managers, and anyone who regularly works with paper.

What Is GSM?

GSM stands for grams per square meter (g/m²) and is the international standard for measuring paper weight. It represents the weight of a single sheet of paper that measures exactly one meter by one meter. Because this measurement is always based on the same fixed area, it is consistent across all paper types and directly comparable. A higher GSM number always means a heavier, thicker sheet of paper.

Standard office copy paper typically falls in the 75–90 GSM range. Lightweight newsprint is around 45–52 GSM, while thick card stock used for business cards or packaging can reach 300–400 GSM. Because GSM is unambiguous and universal, it is the preferred unit in Europe, Asia, and most of the world outside the United States.

The US Basis Weight System

The United States uses a different approach called "basis weight" or "substance weight." Basis weight is defined as the weight in pounds of 500 sheets (one ream) of a specific paper type cut to its designated standard size — called the basis size. The problem is that different paper categories have different standard basis sizes, which is why a "20 lb" bond paper and a "50 lb" text paper can actually be nearly identical in physical weight per sheet.

This system developed historically as paper manufacturers categorized paper by its intended use — writing paper, printing paper, cover paper, index cards — and each category was weighed in its own native sheet size. The result is a system that works well within a single category but causes significant confusion when comparing across categories.

Bond Paper (17 × 22 inches)

Bond paper, also called writing paper or ledger paper, uses a basis size of 17 × 22 inches (374 square inches). This category includes copy paper, stationery, letterhead, and forms. Standard office copy paper is typically 20 lb Bond (approximately 75 GSM) or 24 lb Bond (approximately 90 GSM). Premium letterhead is often 24–28 lb Bond.

The 17 × 22 inch sheet can be cut into four standard 8.5 × 11 inch letter-size sheets, which is one of the reasons this basis size was chosen historically. When you see copier paper labeled "20 lb," this refers to 20 lb Bond weight.

Text Paper (25 × 38 inches)

Text paper, also called book paper or offset paper, uses a basis size of 25 × 38 inches (950 square inches). This category includes paper used for book pages, brochures, catalogues, and magazine interiors. Because the basis area is 2.54 times larger than bond paper, text weights are correspondingly larger numbers for equivalent paper.

A 50 lb Text paper is roughly equivalent to 20 lb Bond — both weigh approximately 74–75 GSM. Text weights typically run from about 40 lb to 120 lb for standard commercial printing applications.

Cover Paper (20 × 26 inches)

Cover paper uses a basis size of 20 × 26 inches (520 square inches). As the name implies, this stock is designed for book and brochure covers, business cards, postcards, and other applications requiring stiffness and durability.

A 65 lb Cover stock weighs approximately 176 GSM, which is a popular weight for business cards and brochure covers. At 80 lb Cover (approximately 216 GSM), the paper is robust enough for most cover applications. Heavy cover stock at 100–130 lb (270–350 GSM) approaches the territory of light cardboard.

Index Paper (25.5 × 30.5 inches)

Index paper uses a basis size of 25.5 × 30.5 inches (777.75 square inches). Originally developed for index cards and tab dividers, this category encompasses stiff, smooth-surfaced papers used for file folders, report covers, and cards requiring durability without being as thick as cover stock.

Common index weights include 90 lb Index (approximately 163 GSM) and 110 lb Index (approximately 200 GSM). Index paper has a slightly different surface finish than cover stock, making it well-suited for applications that need to withstand repeated handling.

The Conversion Formula

Converting between GSM and basis weight uses a straightforward formula based on the basis sheet area. To convert from basis weight to GSM: GSM = basis_weight × 1406.5 ÷ basis_area_in². To convert from GSM to basis weight: basis_weight = GSM × basis_area_in² ÷ 1406.5. The constant 1406.5 is derived from the relationship between grams, pounds, and the number of sheets in a ream.

For example, 20 lb Bond paper: 20 × 1406.5 ÷ 374 = 75.2 GSM. Or to find the Text equivalent of 80 GSM: 80 × 950 ÷ 1406.5 ≈ 54 lb Text. This is why this converter always shows all five system values simultaneously — seeing them together reveals how dramatically the numbers differ while the physical paper remains the same.

Practical Tips for Choosing Paper Weight

For everyday office printing, 75–80 GSM (20 lb Bond) is the standard. For documents that need a more substantial feel — presentations, proposals, resumes — stepping up to 90–100 GSM (24–28 lb Bond) is a common choice. Brochures and flyers typically use 130–170 GSM coated paper for vibrant color reproduction.

Business cards are most commonly printed on 300–350 GSM (100–130 lb Cover) stock. Postcards and greeting cards typically use 270–300 GSM. When working with a printer, confirming specifications in GSM eliminates ambiguity — especially when coordinating with suppliers in different countries who may use different basis weight categories.