How many pieces of paper can I mail with one stamp?

Because a single sheet of 8.5-inch by 11-inch 20-pound paper weighs 0.16 ounce, it is possible to mail a total of five pieces of paper in a standard business-size envelope with a single first-class postage stamp.

The total weight of six sheets of paper at 0.16 ounce each is .96 ounce, or just under the 1 ounce allowed for mailing with a first-class postage stamp. A standard business-size envelope is approximately the same weight as a piece of letter paper, once opened. Because the weight of the envelope must be included in the overall postage, the final count for one stamp is five pieces of paper inside the envelope.