Term: Paper Weight

The thickness of paper is measured by its weight; the more the paper weighs, the thicker the paper is. The weight is determined by how many pounds one ream of paper weighs (approximately 500 sheets). If a paper comes in different sizes, its weight varies even if the thickness is the same. This inconsistency in measurement has led to the use of an additional metric measure (that is, grams per square meter or gsm). When paper is measured in gsm, its weight value does not change with the size of the sheet.

Some typical weights of watercolor paper are 90 lb (190 gsm), 140 lb (300 gsm), and 300 lb (638 gsm). The weight to use depends on what an artist wants to accomplish. For instance, 90 lb paper works well for drawing but it buckles when wet. 140 lb paper can be stretched to avoid buckling, but it dries quickly and can only endure so much scrubbing. Paper of this thickness is often sold as a block of stacked sheets called watercolor blocks that allow the sheets to be wet without being stretched. 300 lb paper is stiff enough that it doesn't require stretching at all, but it absorbs more water and stays wet longer.