Question: how do you know how much postage to put on an envelope?
Answer: First Class Postage The amount of stamps you need on a letter depends on the weight of a letter and delivery method. Letters are typically 1-3 ounces. A 1-ounce letter requires ONE first-class stamp, which increased in price in January of 2019 to $0.55. From there, each additional ounce is another $0.15.