Last updated 2 months ago. Our resources are updated regularly but please keep in mind that links, programs, policies, and contact information do change.
Figuring out the right amount of postage for a letter or package can feel like solving a puzzle.
The number of stamps you need depends on four key factors: the mailpiece’s size, shape, weight, and destination. Get any of these wrong and you’ll face the frustration of returned mail or the unnecessary cost of overpaying.
This guide serves as a resource to master the process. All prices and rules cited are based on the official United States Postal Service rate changes scheduled to take effect on July 13, 2025.
The landscape of postal pricing has shifted dramatically. As part of its 10-year “Delivering for America” plan, the USPS has moved to a more frequent, often twice-yearly, schedule for price adjustments. This strategy aims to better align the agency’s revenue with its operational costs and the rate of inflation.
For mailers, this means the era of static postage rates is over. The cost to mail a letter can change every six months. For those who wish to track these changes directly, the official USPS Postal Explorer website is the ultimate source of truth.
At-a-Glance Price Summary
For quick reference, here are the costs for the most common mailing needs effective July 13, 2025:
| Mail Item | Postage Cost |
|---|---|
| First-Class Mail Forever Stamp (1 oz. letter) | $0.78 |
| Each Additional Ounce (for letters) | $0.29 |
| Domestic Postcard | $0.62 |
| First-Class Mail Flat (Large Envelope, 1 oz.) | $1.63 |
| Global Forever Stamp (1 oz. international letter) | $1.70 |
The Foundation of First-Class Mail
What is a Forever Stamp?
The cornerstone of modern postage is the Forever Stamp. A Forever Stamp is a non-denominational postage stamp, which means it doesn’t have a specific monetary value printed on its face. Instead, its value always equals the current First-Class Mail rate for a standard one-ounce letter on the day it’s used, regardless of the price paid when purchased.
Introduced in 2007 at a price of 41 cents, the Forever Stamp program was designed to offer convenience and stability for consumers amidst fluctuating postal rates. Since 2011, nearly all First-Class stamps sold by the USPS are Forever Stamps.
As of the rate change on July 13, 2025, the value of a single domestic Forever Stamp will be $0.78.
Hedging Against Inflation
The primary advantage of the Forever Stamp is its ability to act as a hedge against future price increases. If you purchase Forever Stamps at the current rate of $0.73 before the July 13, 2025, price hike, each of those stamps will automatically be worth the new $0.78 rate for mailing a one-ounce letter afterward.
For individuals and small businesses that send mail regularly, stocking up on Forever Stamps before a planned rate increase is a simple and effective way to save money.
Global Forever Stamps
The USPS offers an international equivalent called the Global Forever Stamp. This stamp simplifies international mailing. A single Global Forever Stamp provides sufficient postage to send a one-ounce letter or postcard to any country with which the United States maintains mail service.
Like its domestic counterpart, the price of the Global Forever Stamp is also subject to rate adjustments. Effective July 13, 2025, the price and value of a Global Forever Stamp will increase from $1.65 to $1.70.
The Standard Letter
The most common and cost-effective piece of mail is the “standard letter.” This is a mailpiece that meets a specific set of USPS criteria, allowing it to be processed by high-speed automated machinery and requiring only a single Forever Stamp.
Check the Weight
A single domestic Forever Stamp covers the postage for a letter weighing up to and including 1 ounce. To put this in practical terms, 1 ounce is approximately the weight of four sheets of standard 8.5″×11″ paper plus a standard business-sized (#10) envelope.
A typical empty #10 envelope weighs about 6.75 grams (roughly 0.24 ounces), and a single sheet of office paper weighs about 4.5 grams. For anything more than a few pages, it’s always best to weigh your letter on a postal scale to be certain.
Check the Size and Shape
To qualify for the standard letter price, the mailpiece must be rectangular. Square, circular, or other oddly shaped envelopes will require additional postage. The dimensions must fall within a specific range as defined by the USPS Domestic Mail Manual.
Standard Letter Dimensions
| Dimension | Minimum | Maximum |
|---|---|---|
| Height | 3½ inches | 6⅛ inches |
| Length | 5 inches | 11½ inches |
| Thickness | 0.007 inch | ¼ inch |
A standard #10 business envelope, which measures 4⅛ inches high by 9½ inches long, fits comfortably within these parameters.
Calculating Postage for Heavier Letters
The maximum weight for any item to be mailed at First-Class Mail letter rates is 3.5 ounces. Any letter weighing more than this is automatically classified and priced as a “flat” (large envelope), which is significantly more expensive.
For letters that weigh more than 1 ounce but are still under the 3.5-ounce limit, you must add extra postage. Effective July 13, 2025, the cost for each additional ounce (or any fraction of an ounce) is $0.29.
A common and costly mistake is to simply add a second Forever Stamp to a letter that is slightly over one ounce. This leads to significant overpayment. For example, a 2-ounce letter requires $0.78 (for the first ounce) + $0.29 (for the second ounce), for a total of $1.07. Using two Forever Stamps would mean paying $1.56, an overpayment of $0.49.
The USPS sells “Additional Ounce” stamps specifically for this purpose to help you pay the exact amount required.
First-Class Letter Rates (Effective July 13, 2025)
| Weight Not Over | Postage Due | How to Pay with Stamps |
|---|---|---|
| 1 ounce | $0.78 | 1 Forever Stamp |
| 2 ounces | $1.07 | 1 Forever Stamp + 1 Additional Ounce Stamp |
| 3 ounces | $1.36 | 1 Forever Stamp + 2 Additional Ounce Stamps |
| 3.5 ounces | $1.65 | 1 Forever Stamp + 3 Additional Ounce Stamps |
When Standard Rules Don’t Apply
The Non-Machinable Surcharge
The low price of a First-Class stamp is made possible by the USPS’s vast network of high-speed automated sorting equipment. When a letter has characteristics that prevent it from being processed by these machines, it must be sorted by hand, which is a slower and more expensive process. To cover this extra cost, the USPS applies a non-machinable surcharge.
Identifying a Non-Machinable Letter
A letter is considered non-machinable and requires extra postage if it meets one or more of the following criteria:
It is square or has an unusual aspect ratio. A common example is a square wedding invitation. In technical terms, the length divided by the height is less than 1.3 or more than 2.5.
It is too rigid. The letter does not bend easily. This often happens when a plastic gift card or other stiff object is enclosed.
It has lumps, bumps, or an uneven thickness. This can be caused by items like a coin, a house key, or a decorative wax seal on the envelope.
It has a clasp, string, button, or similar closure device. These items can snag and damage the sorting machinery.
It is enclosed in a plastic wrapper. The surface must be paper to be machinable.
The delivery address is written vertically. The address must be oriented parallel to the longest side of the envelope.
Calculating the Extra Cost
The domestic non-machinable surcharge is $0.46. This fee is a flat charge added on top of the regular postage due based on the letter’s weight. It’s a one-time fee per mailpiece, not a recurring charge for each ounce.
Common Non-Machinable Scenarios (Effective July 13, 2025)
| Scenario | Base Postage (by weight) | Surcharge | Total Postage |
|---|---|---|---|
| Square Wedding Invitation (1 oz) | $0.78 | + $0.46 | $1.24 |
| Rigid Photo Mailer (2 oz) | $1.07 | + $0.46 | $1.53 |
| Greeting Card with Wax Seal (1 oz) | $0.78 | + $0.46 | $1.24 |
The USPS sells a specific stamp to cover the cost of a 1-ounce non-machinable letter. After the July 2025 rate change, this stamp will hold a value of $1.24.
Beyond the Letter
Mailing a Postcard
To qualify for the lower postcard rate, a mailpiece must be rectangular and meet very specific dimensions:
- Height: Between 3½ inches and 4¼ inches
- Length: Between 5 inches and 6 inches
- Thickness: Between 0.007 inch and 0.016 inch
If your mailpiece is larger than these dimensions, it will be charged at the more expensive letter rate. Effective July 13, 2025, the postage for a standard domestic postcard will be $0.62.
When Your Envelope is a “Flat”
“Flat” is the official USPS term for a large envelope, newsletter, or magazine. A mailpiece is classified as a flat if it exceeds any one of the maximum dimensions for a standard letter (more than 6⅛ inches high, 11½ inches long, or ¼ inch thick).
To qualify for flat pricing, the item must also meet the following criteria:
Maximum Dimensions: No more than 12 inches high, 15 inches long, and ¾ inch thick.
Flexibility and Uniformity: The envelope must be flexible and uniformly thick. If it’s rigid, lumpy, or contains an object that makes its thickness uneven, it will be charged at the much higher package rate.
A key piece of advice for saving money is to fold your documents if possible. If the contents of a large 9″ x 12″ flat can be folded to fit into a standard #10 business envelope, you’ll pay the lower letter rate, potentially saving a significant amount of money.
Postage for Flats
The maximum weight for a First-Class Mail flat is 13 ounces. Any flat weighing more than this must be sent using a package service like USPS Ground Advantage or Priority Mail.
The pricing for flats is calculated by weight. Effective July 13, 2025, the price for a 1-ounce flat will be $1.63, and each additional ounce will cost $0.27.
Sending Mail Across Borders
Mailing a letter to another country is straightforward, especially if it’s a standard size and weight.
The Simple Method: The Global Forever Stamp
The easiest way to send a standard international letter is with a Global Forever Stamp. One of these stamps, which will cost $1.70 as of July 13, 2025, is sufficient for a standard-sized, rectangular letter weighing up to 1 ounce, sent to any destination country.
Mailing Heavier or Non-Standard International Letters
For international mail that weighs more than 1 ounce or is non-machinable, the pricing becomes more complex. Unlike domestic mail, the cost for additional weight depends on the destination’s country price group. Furthermore, there’s a separate international non-machinable surcharge of $0.49, which is different from the domestic surcharge.
Because of these complexities, for any international mailpiece other than a simple 1-ounce letter, the safest and most reliable method is to use the official USPS International Price Calculator or visit a Post Office retail counter to ensure you apply the correct postage.
When Your Mail Becomes a Package
There’s a clear dividing line where a mailpiece is no longer a letter or a flat and must be sent as a package. This transition is typically triggered by one of the following conditions:
- The item is more than ¾ inch thick at any point
- The item is rigid and not flexible
- The item weighs more than 13 ounces (for First-Class Mail flats) or 3.5 ounces (for First-Class Mail letters)
How Package Postage is Calculated
Once an item is classified as a package, its postage is determined by a different set of rules involving three main variables:
Weight: The heavier the package, the more it costs. Services like USPS Ground Advantage and Priority Mail can handle packages up to 70 lbs.
Destination “Zone”: The United States is divided into shipping zones based on the distance from the origin ZIP code. A package traveling a long distance (e.g., from Florida to Oregon, a high zone number) will cost more to ship than a package traveling a short distance (e.g., from Florida to Georgia, a low zone number).
Dimensions (and Dimensional Weight): For large but lightweight packages, the USPS may charge based on “dimensional weight” (DIM weight). This means you’re paying for the amount of space the package occupies on a truck or plane, not just its physical weight. If a package is larger than 1 cubic foot, its DIM weight is calculated, and if that’s greater than the actual weight, the higher price applies.
The Rise of Surcharges and Nonstandard Fees
In recent years, the USPS has increasingly implemented specific fees for packages that are difficult to process through its automated systems, a practice similar to that of private carriers. This is a strategic move to more accurately price the true cost of handling items that disrupt the efficiency of the sorting network.
For mailers, this means that simply weighing a package is no longer sufficient to determine its cost. The shape and dimensions are now critical factors. For example, starting in July 2025, mailing a poster in a round tube will incur a nonstandard fee, whereas mailing the same poster in a rectangular box of the same weight would not.
To avoid surprise fees, be aware of these common surcharges:
Nonstandard Length: A fee of $4.00 or more applies to packages over 22 inches long.
Nonstandard Characteristics: A $4.00 fee applies to items like tubes, rolls, or certain items containing liquids.
Nonstandard Volume: A significant fee applies to packages larger than 2 cubic feet.
The clear takeaway is to always use standard, rectangular boxes for shipping whenever possible to avoid these additional costs.
Official Tools and Essential Context
With rates and rules subject to change, knowing where to find official information is essential.
The Ultimate Tool: The USPS Postage Price Calculator
For any situation where you’re uncertain about the correct postage, the single best resource is the official USPS Postage Price Calculator. This online tool is always updated with the latest rates and will provide a precise postage cost after you enter the mailpiece’s destination, weight, shape, and dimensions.
The Source of Truth: Postal Explorer and Notice 123
For advanced users, businesses, or anyone who wants to see the complete, official price lists, the USPS maintains the Postal Explorer website. This is the official repository for all mailing standards and regulations, including the full price list known as “Notice 123.”
The Bigger Picture
The U.S. Postal Service’s Mission
To better understand why postage rates are structured the way they are, it helps to know a bit about the unique role of the USPS. As an independent agency of the executive branch, the Postal Service operates under a special mandate.
Universal Service Obligation: The USPS is required to provide postal services to every address in the United States and its territories. A core part of this obligation is that the price of a First-Class Mail stamp is the same for everyone, regardless of their geographic location. A letter sent from a remote village in Alaska to Miami costs the same as a letter sent across town in Chicago.
Self-Funding: A common misconception is that the USPS is funded by tax dollars. In reality, the Postal Service generally receives no tax revenue for its operating expenses. It relies on the sale of postage, products, and services to fund its vast operations, which deliver more mail and packages than any other post in the world. This business-like model is a primary driver behind the need for periodic price adjustments to cover costs and ensure financial stability.
Our articles make government information more accessible. Please consult a qualified professional for financial, legal, or health advice specific to your circumstances.
