If you have purchased paper in the last five years, you’ve noticed more and more manufacturers are using gsm (grams per square meter) instead of weight in pounds. I’ve seen a lot of conversion scales, and I became curious how the conversion is made.
Then I became curious how we measure the pound weight of paper anyway. Here’s what I found (and why gsm is the more accurate way to know how heavy paper stock is.
Papers come in different weights–letter weight, cover stock, card stock. But there is more than use that describes paper–there is weight. You’ve seen paper stock printed in three ways–in pounds (60-lb. or 60#), grams per square meter (g/m2 or gsm), or points (pts). There seems to be a big difference. There is. Even if you don’t love the metric system, you’ll find the gsm method more reliable.
Pounds measure weight, no matter what the size. The pound weight of paper is set by the weight (in pounds) of a ream of paper–500 sheets. It doesn’t matter how big the paper is– cover stock is cut from a “standard” size sheet that measures 20″ x 26.” Text stock is cut from a “standard” size sheet that 25″ x 38″–considerably bigger. But a ream of 500 sheets, regardless of size, is put on a scale and weighed. That measurement is accurate, but very variable.
Points measure height, no matter what the size. The point size is a bit more reliable. It measures the height of a ream of paper. A 10-pt card stock means a ream of paper (500 sheets) measures 10 inches. In this case, the flat size of the sheet doesn’t matter.
To get a feel for the difference: Most business cards are 10-pt or 15-pt stock, the post office’s minimum measurement for a post card is 7-point stock. A point is 0.007″ or one-one-thousandths of an inch. This is a better measurement for comparison, but it still doesn’t sort out heavy-bulk differences for paper that’s been compressed more.
Gsm measures the weight of a standard size paper. Gsm is the reliable because it is standard across all papers. It measures the weight of a square meter of paper. That sets the size as the constant, and allows the weight to vary by heaviness of paper stock. A square meter of a light stock might be 90 gsm, and a square meter of heavier stock might be 140 gsm. In each case, the size is the same–a square meter.
–Quinn McDonald is a writer, life- and creativity coach who loves paper.