Priority Mail Boxes VS Flat Rate Boxes: Difference Explained

Have you ever wondered what the difference is between Priority Mail boxes and Flat Rate boxes?

Priority Mail boxes(charged based on the weight of the box and the zone) and Flat Rate boxes(charged at a flat fee) are not the same thing. They are charged at different rates, so it is important to establish which is the most economical for the package that you wish to send. Check with a shipping clerk, who should be able to help you work out the best option.

Today we will cover this topic fully so you will have no questions left after you read this article.

What’s The Difference Between Priority Mail Boxes And Flat Rate Boxes?

The main difference between Priority Mail boxes and Flat Rate boxes is the cost.

Priority Mail boxes are charged based on the weight of the box and the zone that they are being shipped to. A Flat Rate box is charged at a flat fee and it will cost you the same regardless of where you are sending it to.

Is It Cheaper To Mail Flat Rate Or Priority?

This depends on where you plan to mail your item to and what it weighs. If your item is small, light, and going to one of the low-numbered zones, it may be cheaper to send your mail via Priority Mail shipping than Flat Rate shipping.

However, if you are sending heavy mail (up to 70 lb.) to one of the zones with a high number, it will often cost less to send it using a Flat Rate. It is important to work out what the shipping cost for Priority Mail is, and compare this with the shipping cost for Flat Rate.

Heavier items will almost always be cheaper to send with Flat Rate shipping, but this rule only kicks in with items that weigh over 21 pounds. If you are sending light packages, it may be cheaper to use Priority Mail shipping, regardless of which zone you are sending it to.

In general, however, if you are sending it to Zone 8 or Zone 9, it is usually cheaper to send it via Flat Rate mail. Check with a shipping clerk, who should be able to help you work out the best option.

Q&A Section

Here are a few top queries about Flat Rate and Priority Mail shipping.

Q: Can I Use A Flat Rate Box For Priority Mail?

You can only use a Flat Rate box to ship something using the Flat Rate service. If you want to send Priority Mail according to zone and weight costs, you will need to use a different kind of box.

USPS provides Flat Rate boxes free of charge, but these can only be used for the Flat Rate shipping service. If you put your items in a Flat Rate box, you will be charged the standard Flat Rate for the size of the box that you use.

Q: Are There Priority Mail Boxes That Are Not Flat Rate?

Yes, there are Priority Mail boxes that do not carry the Flat Rate stamp, and these can be shipped without paying the Flat Rate fee. If your item is light and for a local zone, this is likely to be a better option.

Priority Mail boxes can be used to ship to anywhere in the US, but you will pay more the further your parcel is going.

These boxes come in a variety of sizes, including skinnier boxes and fatter ones. You can get these for free from USPS, and they will have the Priority Mail stamp on them, so you don’t need to add it.

They can be ordered from the USPS site, just like Flat Rate boxes.

Q: Are USPS Flat Rate Boxes Insured?

Yes, there is some insurance on a Flat Rate box. If you do not purchase any additional insurance, you will get $50 automatically on most boxes that you send. If you wish to insure your package for more than this, it is a good idea to speak to a shipping clerk.

You will have to pay extra to add insurance, and in most cases, you can insure a package up to $5000. Make sure you keep your receipt.

Q: Is There A Weight Limit On USPS Flat Rate Boxes?

Yes, but it is very generous. You can ship anything up to 70 pounds, regardless of the box size or fee that you pay. All Flat Rate boxes can contain items up to 70 pounds, and there is no advantage to shipping lighter items because you pay the same rate regardless of what the package weighs.

However, you cannot ship a Flat Rate package that weighs more than 70 pounds, no matter what. There is no option to pay extra to use this service if your package weighs over 70 pounds.

Q: Can I Use A Flat Rate Box But Pay By Weight?

No. If you want to ship by weight, you cannot use a Flat Rate box. The Flat Rate box tells the USPS workers that you want to pay the flat fee for shipping, and trying to use a Flat Rate box will result in you being charged the flat rate.

Do not try to modify a Flat Rate box so that you can use it for shipping by weight. USPS does not allow this, even if you completely cover the words “Flat Rate.”

Choose one of the other Priority Mail boxes instead. USPS offers these for free, and it’s a good idea to have some ready when you want to mail items.

Q: Can Small Flat Rate Boxes Go In The Mailbox?

If you have paid for your postage online and affixed the correct label to the Flat Rate box, you can simply place it in your mailbox for the mail carrier to collect. This is fine for small boxes.

In general, however, it is best to drop your mail off at the local post office so that you know the package has been accepted into the system. You will then be given a receipt to demonstrate that it was posted. Keep this safe in case the package gets lost.


Priority Mail boxes are not the same as Flat Rate boxes, although both will be shipped using the Priority Mail method. They share some similarities, such as insurance and shipping speed, but they are different and you should not use the boxes interchangeably.