Paper weight is often stated in two ways – pounds (lbs) and grams per square metre (gsm or g/m2). These two figures are calculated in slightly different ways and tell us slightly differing information. Here we explain how paper weight is measured.
Paper weight in pounds (lbs)
Measuring paper weight in pounds originates from the United States of America. The figure denotes how much a ream of 500 sheets of a particular paper would weigh if the sheets are cut to its standard size. For example, the standard size for a sheet of watercolour paper is full imperial, which is 22” x 30”, so if you’re looking at a sheet of 140lb weight paper on jacksonsart.com, the figure of 140lb is actually the weight of the 500 full size sheets.
Unfortunately, not all paper is 22” x 30” as standard. And for this reason, a sheet of 80lb drawing paper is not the same weight as a sheet of 80lb watercolour paper, because a standard size drawing paper sheet is 24” x 36” and therefore larger than the watercolour paper.
Grams per square metre (gsm)
Grams per square metre is more straightforward. As the unit name suggests, it tells you what one square metre of the paper would weigh and does not consider standard sizes. Consequently you can compare different types of paper in terms of weight if you look solely at the weight as it is stated in gsm. If we were to return to our example of comparing our 80lb sheet of drawing paper with our 80lb sheet of watercolour paper, the difference in weight is clear when we see that the watercolour paper is 170gsm while the drawing paper is 130gsm.
Recommended papers for painting, drawing and printmaking
The ideal paper weight varies depending on what you intend to do with it. For example the lightest papers at 30 – 90gsm would require less pressure in relief printmaking processes and are often favoured by printmakers who hand burnish their prints. Our lightest available paper is the Kitakata washi by Awagami, just 36gsm and perfect for mokuhanga techniques. Cartridge papers that weigh 100 – 200gsm will be easy to roll and transport home from a life drawing class, but a heavier 200 – 300gsm paper will be more robust and able to take heavier applications of media. Watercolour paper that weighs 300 – 425gsm is the most popular. It is sufficiently robust for all water-soluble media applications and costs less than heavier watercolour papers because less raw materials are used to make each sheet. Papers heavier than 425gsm are less likely to need stretching prior to use. 850gsm+ papers are as stiff as card and could be considered a good alternative to a canvas panel for acrylic painting, or oil if sufficiently primed.