The number of stamps required for an envelope is not fixed; it depends on the envelope’s weight, dimensions, and shape. Determining the correct postage involves matching the envelope’s characteristics to current domestic or international mailing rates. While a single stamp is the most common scenario, many factors can quickly necessitate additional postage. Understanding the requirements for a standard letter provides the baseline for calculating all other mailing needs.
The Standard First-Class Letter
A single Forever Stamp is the standard postage for a domestic First-Class letter, covering the cost for the first ounce of weight. This stamp is designed to always equal the current 1-ounce rate, remaining valid even after price increases. To qualify for this single-stamp rate, the envelope must meet specific size and shape criteria. The envelope must be rectangular, with a maximum length of 11.5 inches, a maximum height of 6.125 inches, and a maximum thickness of 0.25 inches. Any envelope exceeding these dimensions or the 1-ounce weight limit requires additional postage.
Factors That Increase Postage Needs
The two primary factors that increase required postage beyond a single Forever Stamp are weight and non-machinable characteristics. For letters weighing more than one ounce, additional postage is required for each subsequent ounce up to the 3.5-ounce maximum for a standard letter. This additional ounce rate is a fixed cost added to the initial 1-ounce rate. For example, a 2-ounce letter requires the initial Forever Stamp value plus the cost for one additional ounce.
An envelope may also incur a non-machinable surcharge, which is an extra fee applied when the mailpiece cannot be processed automatically by sorting equipment. This surcharge applies even if the letter is under the 1-ounce weight limit. Common examples include square envelopes, rigid envelopes, or those containing lumpy items like keys or decorative clasps. Since these items must be sorted manually, the surcharge is applied. To cover the non-machinable surcharge, an extra stamp or equivalent postage must be added.
Mailing Beyond the Standard Letter
When an envelope exceeds the maximum dimensions for a standard letter, it is classified as a large envelope, also known as a “Flat.” Flats are subject to a higher initial postage rate than standard letters, even for the first ounce. They have different weight increments and maximum dimensions than standard letters. Since the rates for Flats are more complex and vary based on weight and size, it is advisable to use an online postage calculator or consult a postal service employee for the precise rate.
Sending a letter internationally requires a different approach, as domestic Forever Stamps are insufficient to cover the cost. For most 1-ounce letters sent to any country, the simplest solution is to use a Global Forever Stamp. This specialized stamp covers the single-piece 1-ounce First-Class Mail International rate, regardless of the destination or future rate increases. Although it is possible to use a combination of domestic Forever Stamps and smaller denomination stamps to meet the international rate, the Global Forever Stamp provides a single, convenient option.