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More Than Standard Envelopes: How Does USPS Postage Deal with Postcards, International Letters, and Overweight Mail? [A Practical Guide for 2025]
Do you also think that sending a letter, as long as you stick a few forever stamps on it , everything will be fine? If you think so, you are too naive! Sending letters, especially those “non-standard” mails – such as postcards sent to distant friends, international letters across mountains and seas, or overweight mails that accidentally stuffed too many photos – have their own set of postage rules.
If your letter has been returned due to insufficient postage, or you have been waiting for the mail but it has not arrived, it is likely that something went wrong in the postage process. Don’t worry, this 2025 USPS Postage Advanced Guide is here to help you sort out the correct way to open these “non-standard” mails, and I will also quietly tell you some practical money-saving tips!
What is the most cost-effective way to send postcards?
Many people have a misunderstanding that since postcards are so light, a forever stamp is enough. This is totally wrong! USPS has designed a special stamp specifically for postcards – Postcard Stamp .
Postage rates (from July 2025) :
| type | weight limit | Size requirements | postage |
| postcard | ≤ 1 oz | 5″×3.5″ to 6″×4.25″, thickness 0.007″–0.016″ | $0.61 |
Be careful! Oversized “postcards” will cost you extra money. Remember, if your postcard is oversized, even if the weight meets the postcard standard, USPS will treat it as a standard letter, and you will need to use the $0.78 forever stamp . This is real extra money! The value of a stamp is reflected in this way.
Recommendation : It is safer to purchase postcards that are officially or certified printed by USPS, which can effectively avoid additional costs caused by size errors.
How to stamp international letters?
Want to send a letter abroad? It may sound complicated, but it’s actually not that difficult if you choose the right type of stamps.
International standard letter:
| Email Type | weight limit | Stamps Required | Cost (2025) |
| International letters or postcards | ≤ 1 oz | Global Forever Stamp | $1.70 |
| More than 1 oz | – | First-Class Package Int. | Pricing by country/weight |
Tips : One of the great advantages of the Global Forever Stamp is that it is universal and can be used to mail to more than 190 countries and regions around the world. This globally universal stamp is really very convenient. So, next time you send a postcard or letter to a friend overseas, don’t be silly and put a forever stamp on it , it doesn’t count!
How to deal with overweight letters?
Even for domestic mail, if you stuff photos, keys, USBs, or even just 4 pages of documents in the envelope, it is likely to exceed the 1 ounce weight limit. At this time, a single forever stamp is not enough!
Calculation method for overweight mail charges:
1st oz: $0.78 (equivalent to the value of 1 forever stamp )
Each additional 1 oz: + $0.29 (You need to apply Additional Ounce Stamp )
Remember, the maximum weight of a USPS standard letter is 3.5 oz . If your letter weighs more than this, it cannot be sent as a regular letter and must be sent as a **Flats (large envelope)** or a parcel.
What to do if the size exceeds the standard? Don’t let your letter be “unique”!
| Condition | Additional fee range |
| Too thick/ irregular shape | $0.40 – $4.50 |
Tip : If your letter is too thick or irregularly shaped to be processed by the machine, USPS will charge a “non-mechanical handling” surcharge. To avoid mail being returned or delayed, it is best to directly purchase the “non-mechanical handling” additional stamps provided by USPS. A correct stamp can save you a lot of trouble.
Three practical weighing methods let you say goodbye to “blind testing”!
Are you still judging the weight of a letter by feel? That’s too unreliable! The following three methods can help you accurately grasp the weight of the mail and avoid insufficient or wasted postage.
Home electronic scale (0.1 oz accuracy) : The most convenient and practical tool, suitable for weighing the total weight of ordinary letters and contents.
USPS self-service terminal : The self-service machine in the post office provides weighing and label printing functions, which is very convenient.
USPS App/Online Tool : With the official tool, you can estimate postage and get recommendations for stamp combinations.
Actual reference weight, so you don’t panic:
| thing | Weight (approx.) |
| A4 paper (1 sheet) | 0.16 oz |
| Empty envelope | 0.20 oz |
| credit card | 0.05 oz |
| Photos (5 photos) | 0.80 oz |
4 practical tips to save postage and spend your money wisely!
It is more economical to use a combination of stamps : Remember what I said before? The total price of $0.78 (1 forever stamp ) + $0.29 (1 additional ounce stamp) is $1.07 , which is much more cost-effective than directly sticking two forever stamps ( $1.56 )! Choosing the right stamp combination is crucial.
Bulk purchase discounts : When you buy USPS stamps at membership stores such as Costco and Sam’s Club, you can sometimes enjoy a 5%-8% discount, which can add up to a considerable amount.
Use an electronic postage platform : Platforms like Stamps.com provide printing labels and accurate billing functions, which are particularly suitable for small businesses or users who send mail frequently.
Pay attention to USPS price adjustment notices in advance : USPS usually adjusts postage in January and July every year. Stocking up on tickets in advance can help you save money.