As of June 2014, it costs 70 cents to mail a standard letter weighing 33.5 grams within the United States. The exact number of stamps required varies based on the value of each individual stamp placed on the envelope. The sender could use one 70-cent step or two 49-cent stamps.
The United States Postal Service uses ounces as the basis of its pricing, not grams. The letter's weight of 33.5 grams converts into 1.182 ounces. Since 1.182 ounces is more than 1 ounce and less than 2 ounces, the price is 49 cents for the first ounce and 21 cents for the second portion of an ounce, or a total of 70 cents.
In addition to adhesive stamps, other postage payment options are available. When using metered mail or an online service such as Stamps.com, the price for the first ounce is reduced slightly to 48 cents. The total price in this case would be 69 cents.