How Many Stamps per Ounce/Ounces for One Stamp? Solved

Short Answer: One $0.55 First-Class Mail stamp covers one ounce. However, you do not need one stamp per ounce. First-Class Mail prices anything above one ounce at an additional $0.15 per ounce ($0.70 for two ounces, $0.85 for three ounces, etc.), and you can purchase Additional Ounce stamps for $0.15 each. For more details about how many stamps to use, see below.

How Many Stamps per Ounce/Ounces for One Stamp?

One First-Class Mail stamp (including Forever stamps) costs $0.55 and covers one ounce. However, this does not mean you need one $0.55 stamp per ounce when sending letters or packages.

You can use United States Postal Service (USPS) First-Class Mail stamps for letters up to 3.5 ounces, and the price will increase $0.15 with each ounce ($0.70 for two ounces, $0.85 for three ounces, and $1 for 3.5 ounces).[1]

Note that even though the price per ounce is not equivalent to using one stamp per ounce, you should not cut any of your stamps in halves or thirds and add a partial stamp to your package. This will only invalidate the stamp. Instead, use one of the following options:

  • Use one Forever stamp, then pay the remainder of the postage at the post office counter when you mail the letter.
  • Use one Forever stamp and purchase First-Class Mail Additional Ounce stamps ($0.15 each) to cover the remaining postage.[2]

Our related research lists where to buy stamps.

Postage for Large Letters and Postcards

Letters larger than 3.5 ounces are considered large envelopes and anything over 13 ounces is considered a parcel.[1] Letters and packages of these types are priced differently than stamped letters based on their weight, shipping method, and destination. If you know how much your envelope weighs, you can use the U.S. Postal Service’s postage rate calculator to determine how much you’ll have to pay.

Postcards are also priced differently than letters and cost $0.35 each.[1] You can buy postcard stamps that cost $0.35 each rather than using a standard or Forever stamp.[3]

Additional Costs for International Mail

It costs $1.20 to send a First-Class Mail letter or postcard that weighs one ounce or less internationally. This includes Canada and Mexico. If your letter weighs more than one ounce, the cost of the postage will vary by country — ranging from $1.20 to $4.32 for letters up to 3.5 ounces.[4]

Where to Place Your Stamp(s)

You should place your stamp on the upper right of the envelope you wish to mail, on the same side where you write the address. If you need more than one stamp, place them all in the upper right corner, but be sure that they do not overlap.

There is no maximum number of stamps you can place on an envelope, but the USPS does require that the stamps not cover the addresses. Keep in mind, too, that your First-Class Mail letter should not exceed 3.5 ounces.[1]

Want to make it easy? See our list of places that sell pre-stamped envelopes.

Costs for Other Classifications of Mail Service

The costs quoted above are for First-Class Mail as defined by the USPS. There are other services available that will get your letter to its destination faster, but these will be more expensive. These services are also suitable if what you are mailing exceeds the 13-ounce First-Class Mail weight limit. See pricing, timing, and more details in the table below.[1]

Classification Fees Timing Best for:
Media Mail $2.80 to $40 (based on weight) 2 to 8 business days Books, DVDs, CDs, manuscripts, loose-leaf pages, and binders
Priority Mail Express $22.75 to $529.80 (based on weight and destination) Overnight Shipments that require fast delivery
Priority Mail $7.02 to $212.19 (based on weight and destination) 1 to 3 business days Customers that want tracking and insurance (both are included)
USPS Retail Ground $7.50 to $202.35 (based on weight and destination) 2 to 8 business days Non-urgent packages and letters over 13 ounces


    • Lindsey Desmet says:
      First Quarter Finance logostaff

      Hello, Karen! Unfortunately, we are unable to provide specific postage estimates. You may want to sign up at JustAnswer, where an expert can provide a thorough answer to your question. (Note that FQF may receive a commission if you sign up at JustAnswer and ask a question.)

  • I have a little box that ways less than 13 ounces. Let’s say it ways 13 ounces, how many forever stamps will I need to put on the box?

    • Kathleen Wilson says:
      First Quarter Finance logostaff

      Hi Jeremy,
      If my calculations are correct, it looks like you’ll need about 7 stamps. Instead of putting stamps on individually, you can go to the post office and just have them weigh your box and then put one stamp on it that covers the full cost. You can also check out the USPS Postage Price Calculator
      for a better idea of how much it will cost — you can put in your zip code, the zip code of where you’re sending the item, the weight, and shape, and get an exact price quote.

  • I’m a little bit confused, in the third paragraph you state that if a package weighs 1oz or less, you can use a forever stamp, but every ounce over that is $.21.., so you go in to say that it would be wasting a forever stamp to put two on there, but what’s the alternative when all you do have is forever stamps?

    • Rebecca Turley says:
      First Quarter Finance logostaff

      Hi Jenna,

      Often times, you can save money by going into the post office and asking them to weigh your package/envelope for you. That way you can pay the exact amount of what it will cost to mail your package instead of wasting money by putting two forever stamps on it when it may be only slightly more than 1 ounce.