The weight of most standard papers used for correspondence is based on the type of paper and how it is produced. Letter-sized bond paper in the U.S. is normally produced in large sheets, each of which is cut down to create four 8-1/2-by-11-inch letter-size pieces. The stated weight is based on the number of sheets before they are cut, so a ream of 20-pound weight paper means 500 sheets weighs 20 pounds. Since each sheet equals four pieces of letter-size paper, your 20-pound baseline in this case is 500 sheets of four pieces each, for a total of 2000 pieces of letter-size paper .
Look at the box or packaging of the letter-size paper you're using to find the weight. Typical bond paper used in most home and office computers is 20 pounds per ream.
Multiply the number of pounds by the number of ounces in a pound: 20 pounds times 16 ounces per pound equals 320 ounces.
Divide the number of ounces by the number of letter-size sheets in a ream: 320 ounces divided by 2,000 pieces of paper gives a per-piece weight of 0.16 ounces.
Count the number of pieces of letter-size paper in the document you need to mail. Multiply this number by 0.16 ounces to obtain the total weight. For example, if your document is five pages, multiply five by 0.16 to get a total weight of 0.8 ounces.
Round the total weight up to the nearest full ounce, then multiply the number of ounces by the per-ounce rate for the type of mail service you've selected. At the time of publication, the first class mailing rate in the U.S. was 44 cents per ounce. Your five-page document weighs just under one ounce, so it can be mailed for 44 cents.
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