how much does a letter weigh
Making the world better, one answer at a time. If you go to the United States Postal Service web-stie, you will find that one US First class stamp ($0.42) will cover the cost to mail a letter that weighs up to 1 ounce, about 28.35 grams. Thus, the average weight of a letter is one ounce or less. If you go to the United States Postal Service web-stie, you will find that one US First class stamp ($0.42) will cover the cost to mail a letter that weighs up to 1 ounce, about 28.35 grams.  Minor edit?