Shipping margins are essential for the sustainability and profitability of any kind of business. And as a business owner, you are probably on the lookout for cheaper shipping charges. One such option is through the USPS flat rate shipping.

While using flat rate shipping, the weight of a package does not affect the charges. So, if you are shipping heavy packages, it means that you will save some money. However, flat rate shipping may be expensive if you are shipping lightweight items.

Continue reading the article to know more about flat rate shipping, how it works, and identify whether it is suitable for your business.

What is flat rate shipping? 

The USPS flat rate shipping is a service offered by the U.S postal service offering 1-3 days single flat rate shipping. This service is attractive to businesses since it doesn’t require that you weigh parcels for calculations of shipping charges.

Why is flat rate shipping ideal for ecommerce stores? 

USPS flat rate shipping is an attractive shipping alternative for several reasons based on how shipping costs are calculated. First, the longer the distance of shipping, the more expensive it is typically. This also increases with the weight of the parcel.

Also, dimensional weight is the most common pricing technique and is calculated by multiplying the width, length, and height of the parcel. Shipping companies like UPS, FedEx, and USPS calculate shipping costs based on the greatest number, the package's actual weight, or the calculated dimensional weight.

A flat-rate option simplifies things and can be the ideal alternative to most brands, especially ones that are smaller and self-fulfill orders.

Remember USPS priority mail flat rate can be a method of calculating for shipping charges when a fixed shipping rate is charged for every order placed instead of providing free shipping or passing real-time shipping rates on customers.

This article purposely talks about the USPS flat rate shipping services.

How flat rate shipping works in three steps.

Flat rate shipping services mean that the costs of shipping are not directly connected with the weight, size, or shape of the shipped packages, hence the name "flat rate." This system depends on how much you put in a special issue USPS box. Ecommerce businesses ship products using this service in the following three steps.

1.Get a USPS flat rate box.

Instead of packages in your box, you can choose from the available USPS flat rate boxes at the nearest post office. There are various sizes you can choose from, and the bigger the box, the more money you'll be charged. The maximum weight allowed is 70lbs.

As your shipment distance and weight of the package increase, the benefits of using USPS flat rate shipping also increase.

2. Pack your items and address them.

After picking the correct box for your items, you can start packing things into it, ensuring that they fit in perfectly.

3. Ship your items.

Drop the flat rate shipping box at the nearest post office and ship the box via USPS priority mail services.

Types of USPS flat rate shipping packaging 

Maybe the only downside of this service is that you must use USPS branded boxes or envelopes. You cannot use USPS priority mail flat rate shipping on your company-branded boxes or envelopes. Check the types of packaging you can use with this service below.

a. USPS priority mail flat rate envelopes.

The USPS flat rate shipping has three types of envelopes available for this service. Some provide better protection than others. The following are the available sizes you can pick from all the measurements are in inches;

  • Priority mail flat rate envelope: 12 ½ L ×9 ½ W.
  • Priority mail flat rate legal envelope: 15 L× 9 ½ W.
  • Priority mail flat-rate padded envelope: 9 ½ L ×12 ½ W.

These envelopes are ideal for jewelry, documents, art, tickets, and most non-bulky items. Also, they will save you from over-weight based priority mail shipping options.

b. Priority mail flat rate small box.

For smaller packages, especially small heavy/dense items that do not fit in the envelopes, mail flat rate small box is an excellent alternative. The U.S postal services describe the sizes as equivalent to three stacked DVD cases.

The boxes have an adhesive flap that has to fully close depending on the folds, meaning that the items should not bulge out and need to fit in tightly. And this applies to all the boxed sets for this purpose.

Ideally, small boxes are perfect for vape supplies, bulkier jewelry, small electronics, and any other items that cannot fit in the envelopes.

c. Flat rate medium box.

People opt for medium boxes over small ones because USPS flat rate medium boxes are available in two different versions. There is the side loading type which is a little bit narrow, and the top-loading type offering a little more space than the former.

The availability of different versions is ideal for accommodating products and items of different sizes.  Though these two versions carry various sizes and the items may also vary widely, they cost the same amounts to ship items using them.

Also, if you decide to use this box size, it is important to compare costs against weight-based shipping. This is so because the latter would sometimes be cheaper than flat rate shipping based on the weight and shipping distance.

d. Flat rate large boxes.

This box type offers great value when you are shipping large heavier, and large items. You will find this option cheaper than weight-based alternatives for items weighing over 25pounds to various zones.

Packages delivered to the long distance across the country will probably be cheaper when using USPS flat rate large boxes based on the weight. These boxes can be used to ship large electronics like computers and sound systems in terms of scale.

One of the benefits of using mail technology is that it allows you to set rules for assigning the types of boxes you can use. For larger products that travel longer distances, you can design rules allowing you to select either flat rate shipping options, or the priority mail services to optimize decision making depending on the weight and distance traveled.

e. USPS priority mail APO/DPO/FPO large flat rate box.

This packaging system is specifically used to ship items to military personnel and troops based overseas. It is the same size as the USPS flat rate large boxes, but it features a message of support and encouragement to the soldiers and offers discounted shipping rates.

The size of the box has the ability to pack approved items within the weight limit of 70lbs. overseas shipping can be a little expensive, and so this option allows you to send things to your loved ones at an affordable price.

What is the USPS regional rate shipping?

This is a shipping option that offers a flat rate of up to 20 pounds based on which types of boxes you select. The only difference between this method and flat rate shipping is that it still factors in the weights of the items.

If you compare this option to both standard priority mail weight-based methods and most priority flat rate services, it will be advantageous sometimes, and at times it will lose. The benefits can be great when it wins, so it is crucial to make comparisons.

For instance, if you compare regional rate box A against medium and large flat rate boxes, the first box will win for almost every zone for up to 15 pounds since that is the minimum limit for regional rate box A.

On the flips side, if you compare the regional rate box B with the large and medium flat rate boxes weighing up to 20 lbs, the regional rate box B takes the lead in zones 1-6, medium flat rates wins in 6-7 while the large flat rate boxes win from zone 8-9.

Similar to the USPS priority mail flat rate medium boxes, the regional rate boxes are available in two forms, boxes A and B.


USPS flat rate shipping is a common service within the U.S postal services that provides a cheaper shipping option. However, it becomes more affordable when your items are heavy enough so that it is cheaper than regular rates.

You can find out if flat rates are ideal for your ecommerce shipping tasks by comparing this service to what you are currently paying when you ship items. If your items are heavier but below the 70-pound mark and the current charges are higher than the flat rate, this service is for you.

Remember, you will be required to use branded USPS packaging like envelopes and boxes, which are available in different sizes and specifications. This is because using flat rate shipping options does not need you to use personal branded packages.