Paper Weight for Book Printing: GSM and LB

Paper weight for book printing is commonly stated in GSM internationally and lb in the United States. These systems use different references, so the numbers cannot be compared without knowing how each one is calculated.

GSM gives the weight of paper over a fixed area. The U.S. lb system changes according to the paper category. A complete specification should therefore state both the weight and whether the paper is Text, Book, Cover or Bond.

GSM and LB Measure Paper Differently

GSM

GSM means grams per square metre. A 100 gsm paper weighs 100 grams when its area equals one square metre.

The reference area remains the same for every paper category. This makes GSM a consistent way to compare coated, uncoated, interior and cover papers.

GSM measures mass per area. It does not directly state paper thickness, stiffness or opacity.

LB and U.S. Basis Weight

In the U.S. system, lb normally means basis weight: the weight of 500 sheets cut to the standard basic size for that paper category. It may also be written with the symbol #, such as 80# Text.

The main categories used in book and commercial printing are:

• Text, Book and Offset: 25 × 38 inches

• Cover: 20 × 26 inches

• Bond and Writing: 17 × 22 inches

Because each category uses a different reference sheet, the category name is part of the weight specification.

For example, 80 lb Text is approximately 118 gsm, while 80 lb Cover is approximately 216 gsm. “80 lb paper” alone does not identify which material is required.

Bond weight sometimes appears in specifications for forms, workbook pages and office-style paper. It should not be treated as the same scale as Text or Book weight.

GSM and LB Conversion Table

The conversions are approximate. Commercial papers are supplied in standard mill weights, so a calculated value may be matched with a nearby available grade.

For example, 60 lb Text converts to approximately 89 gsm and may be compared with a 90 gsm paper. The actual stock should still be confirmed by its mill specification or approved sample.

GSM and LB Conversion Formula

To convert U.S. basis weight to GSM:

GSM = basis weight in lb × 1,406.14 ÷ basic sheet area in square inches

To convert GSM to U.S. basis weight:

LB = GSM × basic sheet area in square inches ÷ 1,406.14

The correct basic size must be selected before using either formula. A GSM value can produce different lb results depending on whether it is converted into Text, Cover or Bond weight.

The calculation provides an equivalent weight. It does not confirm that the resulting grade is commercially available from a particular paper mill.

Paper Weight for Different Book Components

Interior Pages

Book interiors may use coated or uncoated paper, and the weight should always be written together with the paper type.

Text-heavy books commonly use 70–100 gsm uncoated stock. Lightweight books may use lower GSM paper when sufficient opacity and strength are maintained.

More details about cream, lightweight and Bible paper are available on the uncoated book paper page.

Illustrated books commonly use 105–200 gsm coated paper, depending on the page count and required image presentation. The differences between C1S, C2S, gloss, matte and silk stocks are covered in the coated paper guide.

These ranges identify common starting points. They do not replace confirmation of the actual paper grade.

Softcover Covers

Softcover books commonly use 250–350 gsm cover paper. In the U.S. system, this range sits approximately between 92 and 129 lb Cover.

A production specification should use an available commercial grade, such as 270 gsm or 100 lb Cover, rather than treating the approximate conversion as an exact paper name.

The base paper weight should be stated separately from any surface film. For example:

Cover: 300 gsm C2S coated paper with matte lamination

Hardcover Cases

The printed paper wrapped around a hardcover case may use approximately 128–157 gsm coated paper. This wrap is only the visible covering material.

The rigid structure comes from book board or greyboard, which should be specified by thickness in millimetres. A description such as “300 gsm hardcover” does not identify the complete case construction.

Common board thicknesses and their applications are covered in the book board thickness guide.

GSM Is Not Paper Thickness

Two papers with the same GSM can have different thicknesses. Fibre composition, coating, compression and bulk all change the physical caliper of the sheet.

A high-bulk uncoated paper may create a thicker book block than a dense coated paper at the same GSM. The difference can also affect page movement, spine width and the finished feel of the book.

The relationship between weight and caliper is explained in the paper thickness guide.

Final spine width should be based on the actual paper caliper and final page count. The calculation process is covered separately in the hardcover spine width guide.

How to Write a Complete Paper Specification

When confirming paper weight for book printing, identify the component, paper type, weight and surface. If the project uses a U.S. specification, include the full basis weight category.

Text Interior

Interior: 80 gsm cream uncoated book paper, high opacity, black printing on both sides

Illustrated Interior

Interior: 157 gsm matte coated paper, four-color printing on both sides

U.S. Text Weight

Interior: 80 lb Text matte coated paper, approximately 118 gsm

Softcover

Cover: 300 gsm C2S coated paper with matte lamination

Hardcover

Cover wrap: 157 gsm coated paper with matte lamination, mounted over 2.5 mm greyboard

Descriptions such as “80 lb paper,” “heavy interior paper” or “premium cover stock” are incomplete because they do not identify one production material.

For a specific brand or mill grade, include the full product name or technical data sheet. The approved specification should be retained for repeat production.

FAQ

Why does a calculated GSM value not match the paper catalogue exactly?

The conversion may fall between commercially available mill weights. A calculated 148 gsm paper may be compared with a nearby 150 or 157 gsm stock, but the actual available grade should be confirmed before production.

Does lamination change the stated paper GSM?

The listed GSM normally describes the base paper before lamination. Film and adhesive add weight and thickness to the finished cover but do not change the original paper grade.

Different film types and their effect on the finished surface are explained in the lamination for printing resource.

Can coated and uncoated papers with the same GSM replace each other?

Not automatically. They can differ in thickness, stiffness, ink absorption, opacity and surface feel. A replacement should be checked against the required print result and book structure.

Which paper weight should appear on a purchase order?

Use the actual paper grade and GSM confirmed for production. When the order follows a U.S. specification, also include the complete basis weight category, such as 80 lb Text or 100 lb Cover.