One $0.50 first class rate stamp is required for a 6" x 9" envelope weighing up to 1 ounce. You'll have to pay $0.21 for each additional ounce. So, for a weight of 1 to 2 ounces, it will cost you $0.71. For 2 to 3 ounces, it will be $1.41. For more than 3 ounces, the price will be $1.99. The cost of postage varies by country and method of mailing used. It also depends on how large an area you are sending something to. With these tips, you should be able to figure out how much it will cost you to send a message to someone in your address book.