How Many USPS Stamps Do I Need Per Oz?

Have you ever experienced that feeling of worry or dread right before you drop a letter in the mailbox? Maybe you wrote a long letter or included several pictures in an envelope. Whatever the reason, you feel your letter is a bit heavy and worry about having enough stamps.

It’s not a good feeling, especially when you think about having mail returned to you for additional postage. So, if you want to avoid those feelings of doubt and ensure your mail gets delivered the first time, check out our stamp-per-ounce guide!

How Many Stamps Do I Need Per Oz at USPS?

USPS requires 1 domestic Forever Stamp for standard-size envelopes weighing up to 1 ounce. Above this weight, one additional ounce stamp per ounce is required to cover postage. Cent stamps can also be used to cover the extra postage fees. For mailpieces that are over 3.5 ounces, they are priced as large envelopes/flats and follow a different pricing structure.

You probably still have specific questions about how many stamps your letter needs, so follow our guide to get the answers!

How Many Stamps for a 1 Oz Letter?

Mailpieces weighing up to 1 ounce only require 1 domestic Forever Stamp (currently priced at $0.58).

Forever Stamps are non-denominational, meaning they will always cover postage for letters weighing up to 1 ounce, regardless of any changes to postage rates.

While weight is important in knowing how many stamps to attach, your letter must conform to certain dimensions to avoid extra postage fees.

Here are USPS’ guidelines for standard letters:

  • Have a rectangular shape
  • Be at least 3 ½ inches high x 5 inches long x 0.007 inches thick
  • Be no more than 6 ⅛ inches high x 11 ½  inches long x ¼  inch thick
  • Have a uniform thickness (i.e. not have any bumps or bulges)
  • Be flexible/bendable
  • Have an exterior made of paper

Failure to meet these requirements means that your item will be hand-sorted rather than machine-sorted. Adding this step results in a non-machinable surcharge.

USPS currently charges $0.30 for this fee.

You can pay this fee using a special non-machinable stamp (currently priced at $0.88) instead of a Forever Stamp.

Similarly, you can pay the fee through 1 domestic Forever Stamp, 1 additional ounce stamp, and one 10¢ stamp.

How Much Postage Do I Need for a 1.5 Oz Letter?

As mentioned in the previous section, 1 domestic Forever Stamp is enough to cover postage of a letter weighing up to 1 ounce.

This gives you a lot of flexibility when using these stamps.

Unfortunately, it is less flexible if the price is above 1 ounce.

That’s because, even if your letter weighs 1.1 ounces, you’ll have to pay the price for another whole ounce, even though your letter is only slightly overweight.

Put another way, you’ll pay the same amount to send a letter that weighs 1.1 ounces as you would to send a letter that weighs 2.0 ounces.

USPS currently charges $0.20 for each additional ounce over one ounce. Therefore, a letter weighing 1.5 ounces would need $0.78 worth of postage at current rates.

This can be paid for using one of the following combinations:

  • 1 domestic Forever Stamp and 1 additional ounce stamp
  • 1 domestic Forever Stamp and two 10¢ stamps
  • 1 domestic Forever Stamp, one 10¢ stamp, and two 5¢ stamps

How Many Stamps Do I Need for a 2 Oz Letter?

How Many Stamps Do I Need for a 2 Oz Letter? USPS

As long as your letter weighs exactly 2 ounces, you’ll only need to pay $0.78 to cover the postage for the first ounce, plus the additional ounce fee.

Like the previous example, you can cover this postage using different stamp combinations.

Perhaps the easiest is the combination of 1 domestic Forever Stamp and 1 additional ounce stamp.

Remember that if your letter weighs even slightly more than 2 ounces- say 2.1 ounces, for example- you’ll be on the hook for another ounce of postage.

How Many Stamps Do You Need for 3 Oz?

Letters weighing between 2.1 and 3 ounces require $0.98 worth of postage at the current rates. You can pay for this using one of the following methods:

  • 1 domestic Forever Stamp and 2 additional ounce stamps
  • 1 domestic Forever Stamp, 1 additional ounce stamp, and two 10¢ stamps

How Many Stamps Do I Need for 4 Oz?

The previous examples have referred to USPS’ postage fees for First-Class Mail letters.

To be eligible for these rates, items must conform to the size requirements (mentioned above). In addition, they cannot weigh more than 3.5 ounces.

Therefore, if you’re sending an envelope that weighs 4 ounces, you’ll need to look at USPS’ pricing tables for large envelopes/flats.

A 4-ounce envelope currently costs $1.76.

You could pay for this postage in several ways:

  • 3 domestic Forever Stamps and one 2¢ stamp
  • 2 domestic Forever Stamps and 3 additional ounce stamps
  • 2 domestic Forever Stamps, 2 additional ounce stamps, two 10¢ stamps

As you can see, the number of stamps required when you get up to heavier weights can be fairly confusing.

Therefore, we recommend you take your heavier envelopes to the post office and have them print postage.

Not only will you save yourself the hassle of calculating how many stamps to use, but you’ll also ensure that you won’t under- or overpay (something that could delay delivery).

To find out more, you can also read our posts on 14 USPS stamp types, do USPS stamps expire, and what are non-machinable stamps.

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Marques Thomas

Marques Thomas graduated with a MBA in 2011. Since then, Marques has worked in the retail and consumer service industry as a manager, advisor, and marketer. Marques is also the head writer and founder of

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