"My last printer said I used a 24# paper previously. This time I used a 50# paper and the book came out thinner. How can this be?"
Questions like this arise from a lack of understanding of paper basis weights.
This, plus the failure of printers to explain the practical implications of paper weight, can create great frustration and confusion.
The system of paper weights that prevails in North America dates back to medieval Europe. Let’s see if we can shed some light on this arcane system.
It is important to understand the system so that when you hear paper defined as, say, 50# offset, you understand what it means.
For simplicity’s sake we’ll limit our conversation here to the two types of paper that are both most common and most commonly confused.
First, we’ll need to define some terms. The “#” sign is the common abbreviation for pounds.
When we speak of bond or copy paper, we usually mean an economical commodity grade paper suitable for manuals and reports.
Cheaper grades may be labeled as copier or multi-use paper, indicating their suitability for use in both laser and inkjet printers.
Higher grades of bond paper may also be referred to as text or writing papers, and are commonly used for stationary.
You don’t need a calculator to figure paper weights. Just use this handy chart to determine the equivalence of the most common paper weights used for books, manuals, and publications.
Now let’s take a look at the factors used to calculate these weights.
A ream is 500 sheets of paper. Book weight papers are commonly (but not always) ream-wrapped.
No matter how the paper is packaged or priced, a ream means 500 sheets.
Note that paper sold in bulk is usually priced per M (thousand), per cwt (hundred-weight) or per carton, rather than per ream.
If you live in North America, you probably think of 8½” x 11” as the most common paper size.
Even so, every paper type has a specific basis size, which is much larger than letter size and not necessarily a size in which the paper is commonly sold.
Now let’s put all these facts and figures together. The math is actually pretty simple. We’ll use a package of copier paper for our calculations.
One ream (500 sheets) of bond paper in its basis size of 17” x 22” weighs 20 pounds.
One ream of a similar book paper in its basis size of 25” x 38” weighs in at 50 pounds.
If we cut both of these down to the commonly used size of 8½” x 11”, the bond will be labeled as 20# whereas the offset/book will be called 50#.
Both of the resulting letter-sized reams will weigh just 5#, but that has nothing to do with the description!
Depending on the grade, you may not even be able to tell the difference between the two papers.
Some paper mills even label their paper as “20/50#” in a dubious attempt to avoid confusion.
Don’t confuse weight with thickness! Paper thickness varies significantly between different brands of the same weight and grade of paper.
Copresco’s publication TechTopics #16 “Understanding Paper Weights” addresses this topic in much more detail.
Included are definitions and explanations for a wide range of papers, including the confusing world of cover weight papers. TechTopics #16 has just been revised for 2025.
TechTopics is a continuing series of technical bulletins on preparation, digital printing, paper, and binding. Drop us a line to request a complimentary copy.