The number of pages that can mailed with one first class stamp depends on the weight of the paper and the envelope but is typically between five and 20 pieces of paper. The maximum weight for a letter sent with a first class stamp is 3.5 ounces, including the envelope.
As of April 2014, the price of a stamp to send a letter via first class mail in the United States is 49 cents. In order to qualify as a letter for this type of postage, the pieces of paper must fit in an envelope that is 3 ½ inches to 6 ? inches high, 5 inches to 11 ½ inches long and no more than ¼ inch thick. The envelope must also be rectangular.