The United States Postal Service, sometimes abbreviated as USPS, has a variety of rates based on the type of letter or package being delivered, with weight and speed of delivery being particularly important to the overall cost.
- The standard first-class stamp rate (used on standard letter envelopes with a total weight under one ounce) is 55 cents. This is also the current cost of the “Forever” stamp, which can be used for this type of letter today and in the future, even if prices rise. (If you have a Forever stamp that was purchased at a price below 55 cents, it can still be used to send a standard-size letter.)
For standard size letters over one ounce, the rates goes up 15 cents per ounce. For example, an envelope weighing over one ounce but below two ounces would require 70 cents in postage.
Go here for a complete rate listing for all types and weights of letters and packages sent via the USPS. You can also use the Postage Price Calculator to try to find the expected postage rate for any particular letter or package.