A Weighty Issue

February 22, 2012

lbs vs. gsm – which gives you the most accurate picture of paper weight?

Along with texture and tone, thickness must be taken into account when choosing the paper best suited to your chosen media and desired end result.

Ideally, caliper would be used to measure the thickness of a paper as this would give the most accurate measurement. Instead, a paper’s weight is what is commonly used, and yet it is often misunderstood how weight translates to how thick a paper is. It helps to understand how paper weight is measured.

The paper industry measures a paper’s weight in one of two ways: The Imperial system of pounds per ream (lb) and the Metric system of grams per square metre (g/m² or gsm).

The Imperial system of pounds per ream is often found on paper produced or packaged in the U.S. but it can cause some confusion. A ream always consists of 500 sheets however the basis, or uncut, size of a paper can vary greatly. This means a ream of 17″ × 22″ paper and a ream of 24″ × 36″ paper will have two different weights even if each sheet of paper is exactly the same thickness.

The Metric system of grams per square metre provides a more accurate indication of paper thickness as the basis size of the paper is not a factor in its calculation. Instead, it measures the weight in grams of one square meter of a sheet. While grammage doesn’t give you a precise measurement of the thickness (or caliper), it does enable you to know with certainty that a paper listed at 640 gsm will be thicker than a paper with a weight of 400 gsm.

So what does this all mean when you are selecting a paper? If you are able to see and feel a variety of papers while shopping, the listed weight may not be of great concern to you as paper that has the thickness you desire will be more apparent. When that is not possible, always look to gsm. This measurement is universal across all paper types, is the most accurate measurement of a paper’s weight, and a standard indication of the thickness.