Quick answer: One ordinary Forever stamp generally covers an eligible domestic rectangular First-Class Mail letter weighing no more than one ounce. The exact answer changes with weight, dimensions, thickness, rigidity, shape, destination, and mail service.
A Five-Step Postage Decision
- Choose the destination: domestic or international.
- Identify the mailpiece: postcard, letter, large envelope, or package.
- Weigh it after assembly: include every insert and decoration.
- Measure and inspect it: square, rigid, uneven, or unusually thick pieces may be nonmachinable or another mailpiece type.
- Confirm the exact postage: use the USPS calculator before mailing.
Common Examples
| Mailpiece | Starting point | What can change the answer |
|---|---|---|
| Eligible domestic letter up to 1 oz | 1 ordinary Forever stamp | Nonstandard shape, rigidity, dimensions, or added services |
| Domestic letter over 1 oz | One Forever value plus additional postage | Actual weight and current additional-ounce rate |
| Domestic postcard | Postcard rate | Whether it meets postcard dimensions and construction rules |
| International letter or postcard | International rate | Destination, weight, dimensions, and content restrictions |
| Large envelope or package | Not the ordinary one-stamp letter calculation | Dimensions, weight, rigidity, service, and destination |
Can You Use Multiple Forever Stamps?
Yes, their current postage values can be combined. But adding whole Forever stamps can overpay the required amount, and extra stamps do not make an ineligible mailpiece eligible for a service. For international mail, read the international Forever stamp guide.
Rate check: Values on this page were verified on August 9, 2026. Postal prices and mailing standards can change. Confirm the exact amount with the USPS Retail Postage Price Calculator before mailing.
Frequently Asked Questions
How many Forever stamps do I need for a one-ounce letter?
One ordinary Forever stamp generally covers an eligible domestic rectangular one-ounce First-Class Mail letter.
How many are needed for two or three ounces?
Start with the ordinary Forever value and add the current postage required for the extra weight. Use the calculator because nonmachinable characteristics can change the price.
Do square envelopes need more postage?
They can. Square envelopes are among the characteristics that can make a letter nonmachinable.
How many are needed for international mail?
There is no universal count. Calculate the current international postage for the destination and mailpiece, then compare that total with the current value of the stamps you plan to use.
Sources and Retailer Information
Current rate facts are based on USPS price changes effective July 12, 2026. Mailing standards and prices can change; use current USPS tools for the final decision.