Is one stamp enough for a small envelope?

The Quick Answer

The quick answer is: It depends. When sending a standard envelope through the United States Postal Service (USPS), one Forever stamp is enough postage for a standard 1 oz envelope traveling within the United States. However, if the envelope weighs more than 1 oz, is traveling internationally, is an unusual shape or size, or requires extra services like certified mail, additional postage may be required. The sender is responsible for ensuring proper postage when mailing letters and packages.

What is Considered a Standard Envelope by USPS?

The United States Postal Service defines a standard envelope as:

  • Rectangular in shape
  • Between 3-1/2 inches high x 5 inches long and 6-1/8 inches high x 11-1/2 inches long
  • No more than 1/4 inch thick
  • Weighing 1 ounce or less

As long as your envelope falls within these size and weight limits, a single Forever stamp provides enough postage to send it anywhere within the United States.

Forever stamps are always equal in value to the current First-Class Mail 1 oz letter price. As of January 2023, that price is 60 cents. So one Forever stamp covers 1 ounce of postage on a standard domestic envelope right now.

When is More than One Stamp Needed?

You will need additional postage in the following situations:

  • If the envelope is oversized and falls outside the standard size limits
  • If the envelope weighs more than 1 ounce
  • If you are sending the letter internationally
  • If you want to use extra services like certified mail or registered mail

Let’s look at each of these situations in more detail:

Oversized Envelopes

Any envelopes larger than 6-1/8 inches high x 11-1/2 inches long are considered nonstandard or “oversized” by USPS. These envelopes require additional postage beyond a single Forever stamp.

The exact extra postage amount depends on the dimensions and weight. USPS has specific size categories for oversized envelopes:

Size Extra Postage (in addition to 1 Forever stamp)
Larger than 6-1/8 inches high x 11-1/2 inches long up to 12 inches high x 15 inches long $0.20
Over 12 inches high x 15 inches up to 18 inches high x 18 inches long $0.50

So if your oversized envelope fits in the first size category, you would need 1 Forever stamp plus $0.20 for a total of $0.80 in postage.

Keep in mind that additional postage may also be needed if the oversized envelope weighs over 1 ounce. The extra fees are cumulative.

Envelopes Over 1 Ounce

For standard letter-size envelopes weighing over 1 ounce, each additional ounce requires $0.21 in extra postage.

For example:

  • 1.1 ounce envelope = 1 Forever stamp + $0.21
  • 2 ounce envelope = 1 Forever stamp + $0.42
  • 3 ounce envelope = 1 Forever stamp + $0.63

Oversized envelopes weighing over 1 ounce would need postage for the oversize fee plus the additional ounce rate.

You can use a postal scale to weigh your envelope and calculate the exact postage required based on its size and weight. Many post office locations have scales available for public use.

International Mail

Sending a standard 1 ounce letter internationally requires extra postage beyond a single Forever stamp. The rates vary by destination country. Some examples of international postage prices:

  • Canada – $1.45
  • Mexico – $1.45
  • China – $1.45
  • Japan – $1.45
  • UK – $1.45

Heavier letters and larger envelopes will incur additional fees for extra weight and size. The USPS website has a tool to calculate the exact international postage rate based on your destination, weight, size, and services.

Certain countries may have different size and weight limits for letters compared to domestic mail. Be sure to check the specific country standards when mailing internationally.

Extra Services

Optional services like certified mail, registered mail, return receipts, and insurance require extra fees in addition to regular postage:

  • Certified Mail – $4.00
  • Registered Mail – $15.50
  • Return Receipt Electronic – $2.60
  • Insurance up to $50 coverage – $1.80

So if you wanted to send a standard 1 ounce envelope as certified mail, you would need 1 Forever stamp for the postage plus the $4.00 certified mail fee for a total of $4.60.

Insurance values over $50 would incur higher fees. See the USPS website for details on pricing of extra services.

Tips for Ensuring You Have Enough Postage

To make sure your letter or package has sufficient postage before dropping it in a mailbox:

  • Weigh and measure your envelope to determine if it meets standard size and weight limits
  • Refer to the USPS postage price charts if your mail piece is oversized, overweight, or requires extra services
  • Use the USPS Postage Calculator tool online to estimate required postage
  • Take your envelope to the post office and have them weigh it for you to calculate exact postage
  • Purchase additional ounce stamps or Forever stamps as needed for heavier mail
  • Consider adding extra postage as a buffer if the weight is borderline

The post office will return mail without enough postage to the sender, so it is always best to pay a little extra postage if you are unsure. It is the responsibility of the sender to ensure proper postage when mailing letters or packages.

What Happens If You Don’t Use Enough Postage?

If a piece of mail enters the postal system without enough postage, a few things could happen:

  • The mail may be processed but delivered postage-due to the recipient. The recipient would then have to pay the insufficient postage amount plus a postage due service fee before receiving the mail.
  • The Postal Service may return the mail piece back to you marked “Returned for Additional Postage.” You would then need to place new postage on the envelope and re-mail it.
  • In some cases, the letter may be delivered to the recipient with postage due charged upon delivery. This is less common.

To avoid delays and surcharges, it’s always advisable to weigh questionable envelopes and confirm adequate postage before dropping them in a collection box. Forever stamps provide an easy way to cover postage for standard 1 ounce domestic letters so you don’t have to worry about weighing small envelopes.

But for greeting cards, invitations, large envelopes or packages, taking the extra time to verify postage requirements can save you time and money in the long run.

Changes to Postage Rates and Forever Stamps

Postage rates for different types of mail are subject to change. The cost of a First-Class Mail Forever stamp has increased over the years:

Year Forever Stamp Price
2019 $0.55
2022 $0.58
2023 $0.60

When postage rates go up, Forever stamps bought at the old lower prices still maintain their validity to cover 1 ounce of First-Class Mail postage. So you can stock up on Forever stamps when prices are lower to save money in the future as rates increase.

The Postal Service typically announces upcoming postage rate changes several months in advance before they go into effect. Standard postage stamps without the Forever designation would have to be used at their printed value or supplemented with additional stamps to make up a new rate difference.

Alternative Postage Options

Besides traditional stamps, there are some other options for affixing postage to your mail:

  • Postage meters – Allow printing of calculated postage directly onto envelopes or labels
  • Online stamps – Allow purchasing discount stamps and printing shipping labels with QR codes from home
  • Pickup services – Carriers like UPS and FedEx can pick up and deliver your letter by ground transportation
  • Postal kiosks – Allow payment of exact postage using debit/credit cards at self-service kiosk stations

These alternatives may be more convenient and cost-effective for certain types of high volume or commercial mail. But a standard Forever stamp still provides the simplest and most budget-friendly way to send a regular envelope for most residential mail users.


One Forever stamp covers the postage cost for a standard 1 ounce envelope mailed within the United States. Heavier, larger or international letters will require additional postage. Make sure to weigh and measure your envelope and verify rate requirements to avoid insufficient postage returns or fees. Forever stamps remain valid at their original purchased price to cover basic letter postage even when rates increase in the future. With a little care taken to ensure correct postage, a single Forever stamp on a standard envelope is all you need for convenient delivery through USPS.

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