A paper ream is a package of 500 sheets of paper of the same quality and style which have been cut to the same size. Consumers often purchase paper in the form of reams, while printers may work in even bigger volumes. The paper ream is also used as unit of base measurement for calculating the weight of paper, which is a reference to its density. Weight is usually indicated with the pound symbol (#), often on the endcap of a paper ream so that consumers can utilize this information when selecting paper.

The history of the ream is quite interesting. Originally, a paper ream was made up of 20 quires, sheaves consisting of 24 sheets of paper, meaning that a ream actually contained 480 sheets. The definition of “quire” itself has also changed through the ages, but this is an entirely separate issue. To add to the chaos, printers usually purchased reams which contained 516 sheets of paper, to account for potential wastage. Ultimately, many paper companies adopted a 500 sheet standard for their reams of paper, to reduce confusion.

However, it is still possible to find a so-called “short ream” of only 480 sheets. Short reams are more common with fine or unique papers, but they do crop up in the realm of office supplies as well. If you are purchasing paper, check for a label which will indicate whether or not it is a short ream. This can become especially critical if you are purchasing paper by the case, as a case of ten short reams will fall short of the 5,000 sheets of paper one would expect from a case of regular reams.

As discussed above, the paper ream is also used to measure paper density. When writing paper is labeled as 20#, for example, it means that a stack of 500 17 by 22 inch (36 by 56 centimeter) sheets of this paper weighs 20 pounds (9 kilograms). Other types of paper utilize different base sizes. In countries which use the metric system, many paper companies standardize this measurement, using one square meter as the basis size for a ream when determining weight, no matter what kind of paper it is. Weights of paper can get confusing, since the paper is often cut after its weight has determined; this explains why a ream of 35# bond, for example, does not actually weigh 35 pounds (16 kilograms).

The weight of paper is an important concern for many people. Some weights, for example, will not go through regular office printers, while others are too flimsy for certain tasks. Many paper companies offer base styles in a number of weights, allowing people to choose the weight most suited to their purpose, whether it is a formal wedding invitation or a business letter.