USPS Priority Mail Vs Priority Mail Flat Rate: Ending The Confusion

If you’re shipping with USPS, it is important to know the different service options that they have. One of the most often confused mailing services is between USPS Priority mail vs Priority Mail Flat Rate. In this post, we will go over all the similarities and differences so you will know exactly which service is best for you.

What Is The Difference Between USPS Priority Mail Vs Priority Mail Flat Rate?

The simplest way to understand the difference between USPS Priority Mail vs Priority Flat Rate is to think of USPS Priority Mail as the umbrella service for all Priority Mail. USPS Priority mail is a service with a shipping time of 1 to 3 days. This includes regular Priority Mail, Priority Mail Cubic, Priority Flat Rate, and Priority Regional mail.

Regular Priority Mail uses the weight and dimensions of your package and the distance that the package is traveling to determine the shipping price. Priority Mail Cubic uses the cubic volume of your package and the distance it is traveling to determine the price.

USPS Priority Flat rate has a set price with each predetermined box size and type of envelope. You can ship up to 70 pounds, regardless of distance as long as the item fits inside the box or envelope.

USPS Regional Rates use zoning for distances. There are two types of Regional Rate boxes, A and B, to determine the price. Regional Rate boxes have a weight limit of 15 pounds for Regional A and 20 pounds for Regional B.

Read Also: USPS Priority Mail Regional Box Explained

What Boxes Can You Use Sending USPS Priority Mail?

The biggest confusion between USPS Priority Mail versus Priority Flat rate is when it comes to using the right boxes. To use a regular USPS Priority Mail service, you can use USPS Priority boxes from USPS.

This includes the USPS Priority Mail 1092 box, 1096L Box 4, Shoe Box, and other boxes that do not say “Express”, “Flat Rate” or “Regional Rate” on the box. You can also use your own envelopes or boxes to ship as Priority mail. It does not have to say Priority Mail on them to be shipped as Priority Mail.

What Boxes Can You Use Sending USPS Priority Mail Flat Rate?

You can only use USPS Priority Mail Flat Rate envelopes and boxes that are EXCLUSIVELY from USPS. The box must say Flat Rate to ship them with the Flat Rate price. That includes the Flat Rate Envelopes, no matter what kind, and all the Flat Rate box options, Small Medium, and Large.

The same principle applies to using a Priority Regional Rate pricing, whether you’re using Regional A or Regional B boxes. If you’re using your own envelopes or boxes, you cannot ship them using the USPS Priority Flat Rate or Regional Rate option.

Similarly, if you’re using any Flat Rate or Regional envelopes or boxes, you must use the rates corresponding to the envelope or box. You cannot use a Flat Rate or Regional Rate envelope or box to ship regular Priority mail.

However, there is one exception to this rule. If you have reconstructed the Flat Rate Envelope (FRE) or Flat Rate Box (FRB) in some way, you can ship the item as regular Priority mail without having to pay the Flat Rate price.

If an FRE or FRB is presented at the office of mailing and the customer has manipulated or reconstructed it, the container is accepted using weight and zone — not the Flat Rate price. 

USPS Domestic Mail Manual, Post Bulletin Issue 22435

While you can do this, we do not recommend it if you have other options. The reason being is that it is easier to use your own packaging or a non Flat Rate-marked packaging. While you do have the document to support it, not all postal workers may be aware of the USPS DMM Bulletin that says that you can do it. It is better to eliminate any questioning or confusion at the post office to save you time and headache.

If you want to send a package as a Flat Rate, you will have to get the envelopes or boxes from your local post office. If they do not have them in stock, you can order them from, free of charge, and shipped to your door.

USPS Priority Mail Vs Priority Mail Flat Rate: Which Is Cheaper?

So why would you want to use one service over the other? That will entirely depend on what you’re shipping and where you’re shipping to. Flat Rate envelopes and boxes have a specified cost. So if you’re shipping a heavy item that can fit into a Flat Rate envelope or box to long distances such as Hawaii, Alaska, or across the country, that may be the most affordable option.

A Regional Rate box may make sense if you’re shipping an item to the next city over. If you’re shipping a heavy item that could be more compact than a Flat Rate Box or Envelope, Priority Mail Cubic may make more sense. You can use Pirate Ship’s cubic calculator and see what the shipping price would be. Then, you can compare it with Flat Rate pricing.

Pirate Ship Cubic Calculator Here

Remember that Priority Mail Cubic will not be available at your local post office. You can only access this rate using shipping software such as Pirate Ship or Shippo.

Where Can I Get The Cheapest Shipping Rates?

Shipping software will always give you the cheapest USPS rates in general, no matter what shipping service you buy. That is because they use a commercial discount rate instead of the retail rate that you would pay at your local post office counter. We use and recommend Pirate Ship or Shippo. They are absolutely free to use to get USPS discounted rates.

Pirate Ship is easier to navigate and use but they only offer USPS and UPS discounts. Shippo on the other hand offers international and regional carriers that you may not have thought of or heard of. So if you’re a small business sending packages regularly, they’re great to see all your shipping options.

You can also buy postage in the comfort of your own home or office. You will need a  shipping scale and measuring tape to get the weight and dimensions of your package. Once you have your shipping label, you can drop your package off at the post office without ever having to stand in line.

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