How Heavy Can a Letter Be for a First Class Stamp?

Learn about the maximum weight the US Postal Service allows for when sending a letter via First-Class Mail
how heavy can a first class letter be?
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If you’re wondering how heavy a letter can be for a First Class stamp, you’ve come to the right place. USPS gives mailers a little bit of wiggle room when it comes to how heavy First Class letters can be…but if your letter weighs too much, you may need to ship it.

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3.5 Ounces is the Maximum for How Heavy a First Class Letter Can Be

A First Class letter can only weigh up to 3.5 ounces per mail piece. If you need to send papers or documentation that weighs more than 3.5 ounces, a good strategy is to break up your mail into separate, multiple envelopes with their own stamps. Or, you could always ship it all together using a single Priority Mail Flat Rate Envelope!

Pro Tip: A lot of beginners accidentally mix up the terms “mailing” and “shipping” when, in fact, they describe two wildly different things. Learn more about the difference between mailing and shipping.

Forever Stamps Cover the Cost of One Ounce for a First Class Letter

One Forever First-Class Mail stamp represents the postage for sending one (1) ounce of mail. So, a forever First-Class stamp only buys you enough postage for a one (1 oz) ounce letter. Most letters and postcards weigh less than 1 ounce, though, and therefore require only one Forever Stamp. However, if your letter weighs more than that, you’ll need to pay for additional ounce stamps…and we get into that below.

USPS Requires an Extra Stamp for Additional Ounces After 1 Oz

Letters that weigh more than 1 ounce require additional ounce stamps on top of your first Forever Stamp. Here’s what we mean:

If your letter weighs two (2) ounces, you need one Forever stamp and one additional ounce stamp. If your letter weighs three (3) ounces, you’ll need one Forever stamp and two additional ounce stamps.

If your letter hits the maximum amount of 3.5 ounces, USPS will require a total of four stamps (one Forever and three additional ounce stamp), since that extra half-an-ounce needs its own postage stamp to cover it. Any piece of mail that weighs more than 3.5 will need to be shipped instead of mailed, and you can use USPS shipping services such as First Class Package or Priority Mail for that.

The Cost of Stamps

Currently, Forever stamps cost 63 cents each. You use these stamps to send letters via First Class Mail, but keep in mind that USPS raises the price of stamps every so often. However, once you buy them, you’re good to use them literally forever! That means you can buy a Forever stamp today for 63 cents, and use it ten or fifteen years down the line to send a letter with First Class Mail. Just make sure you don’t lose them!

Additional ounce stamps are cheaper than Forever stamps; currently, they are priced at 24 cents. If your letter is two ounces, the total cost to mail it will be 87 cents (one Forever stamp at $0.63 and one additional ounce stamp at $0.24).

You can pick up rolls of Forever stamps at a lot of different locations, including certain drug stores around town, your local Post Office, and of course, on the USPS website.

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  1. Mike

    You should seriously update this article to include information on ‘Additional Ounce’ stamps. Few people will read the comments and will erroneously use two forever stamps when they do not need to.

    For a website know as ‘Shipping School’ getting details like this correct should be important.

    • jen

      great point!

  2. Mary Jacobs

    My envelope is 9″ by 6.25″ and weighs 6 oz. Can you tell me
    how m much that will cost ?

  3. Nichole

    The USPS website clearly states the maximum weight for 1 forever stamp is 1 oz. Nowhere on the USPS website does it indicate a 3.5oz letter limit for a stamp. 🥴

    • P. Hunter

      Hello… yes, I noticed your concern. I believe it is due to poor answering of questions. People will ask, “ How many ?” and USPS keeps answering with this “maximum First Class weight business.” Just so typical of our PO nowadays…. they have gone down so big time in my 71 years. I will say my father predicted this in the 60’s… also I am a sister and sister in law to 2 postmasters. But you cannot count on the P.O anymore… and they were once totally reliable. Regards!

      • ATP. Hunter

        Edit. Just had to add… although I complained.. there is or are few… countries that can compete with us. The price of a stamp is cheaper here and even with the slipping I feel they are going through… our mail delivery system is the best or certainly amoung the best. I have traveled quite a bit and I personally have never seen more efficient or good rate than us. .. or rather the USPS. Let’s hope they never privatized…!then … who knows?!

  4. P

    The way I read the above information is that if you are ONLY using forever stamps, it takes 2 forever stamps. Yes that’s more than is actually required, but if you don’t have stamps worth different amounts, that’s how you do it. It also mentions splitting up a heavier letter so you don’t waste extra money by using a forever stamp when you only needed 20 cents worth.

  5. jack

    This is wrong. You would not need 2 Forever Stamps on the envelope for 2 ounces. Only additional 58 Cents.

  6. jen

    Stamps are 55 not 58 Cents! Also, for each additional ounce you don’t need an extra 55 Cent Stamp! The Rate for additional ounces is less than Rate for first ounce! Come on people.

    • Rockwell Sands

      Hi Jen, thanks for the comment! USPS actually raised Forever stamp prices from 55 cents to 58 cents in the past several months, which you can see on their website:

      • jen

        Hi, I apologize for that. You are correct. But you are wrong that if it weighs 2 ounces, I would need “2 Forever Stamps”. Why would I put an additional 58 Cents on for the other ounce? An additional ounce Costs only 20 Cents.

        • Fred Porenko

          Yes, it’s true that you can add smaller denomination stamps in conjunction with Forever Stamps. But because the author is referring to the use of Forever Stamps, which must being used 1 Stamp for every ounce, he is correct in saying a 2 ounce Letter will require 2 Forever Stamps. And a 3-ounce letter will require 3 Forever Stamps.

          • jen

            Yes but that’s a wasteful way of doing it.

      • jen

        Additional ounce would be 20 Cents


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