Understanding USPS Flat Rate Shipping: Shipping Flat Rate for Ecommerce

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Shipping Flat Rate for Ecommerce is a service provided by USPS that allows online retailers to mail packages using a predetermined flat rate regardless of the weight or size. This gives the retailer assurance that they are not going to be left with any additional costs from their customers, as well as giving them an edge over other competitors who do not offer this type of shipping. The following article will go into detail about what it means to ship flat rate, how you can take advantage of it and why it is so important in today’s ecommerce world.

What is USPS Flat Rate Shipping?

USPS Flat Rate is a service provided by the United States Postal Service that allows online retailers to set a flat rate on all mailings. Flat Rate envelopes and boxes are available in various sizes.

It is an attractive option to online sellers because they can set a predetermined price for all packages up to that size without having to worry about cost overruns due to the weight of each individual parcel. This essentially allows retailers to use one “flat rate” price per package, regardless of the weights and sizes of their goods.

As long as your package is under 70 pounds, it can be shipped using USPS Priority Flat Rate shipping.

How Does it Work?

Flat rate services provided by USPS allow you to pay a fixed price per package no matter its size or weight. In this way, retailers can improve their packaging and shipping costs while giving customers peace of mind that they are paying a fair price for the shipping of their goods. The “Flat rate” refers to the fixed price per package, and with USPS it is only available for Priority Mail Express and Priority Mail packages.

With USPS flat rate shipping, you cannot use your own shipping boxes. Instead you choose from boxes offered by the USPS that come in small, medium, or large sizes. There is also a flat rate envelope. The bigger the box, the higher the shipping cost. Again, the maximum allowable weight is 70 pounds.

Other than that, you package up your items, address the package, and ship it off through USPS like any other shipment.

When Should You Use USPS Flat Rate Shipping?

Flat rate shipping can be a great option for your ecommerce store.

Shipping costs are typically calculated based on the distance or shipping zones your order ships to. The further you are shipping something and the heavier it is, the more expensive shipping is going to be.

Shipping carriers like USPS, FedEx, and UPS also like to use dimensional weight. Commonly referred to as DIM weight, it involves measuring the length times width times height of a package and basing pricing on that. Shipping carriers will use whatever is higher, the DIM weight or the actual weight of a package when determining what to charge you.

USPS flat rate shipping simplifies all of this by giving you a fixed price regardless of DIM weights or actual weights, providing the package is under 50 pounds.

How Much Does USPS Flat Rate Shipping Cost?

The shipping charge is based on the size of the box. The chart below shows prices as of July 20, 2021. For updated pricing, you can visit the USPS website.

Flat Rate PackageShipping PriceDimensions
Flat Rate Envelope$7.40 Commercial Base$7.95 at Post Office & Online12 1/2″ x 9 1/2″
Padded Flat Rate Envelope$8.00 Commercial Base$8.55 at Post Office & Online12 1/2″ x 9 1/2″
Small Flat Rate Box$7.90 Commercial Base$8.45 at Post Office & OnlineOutside: 8 11/16″ x 5 7/16″ x 1 3/4″Inside: 8 5/8″ x 5 3/8″ x 1 5/8″
Medium Flat Rate Box – 1 (top loading)$13.75 Commercial Base$15.50 at Post Office & OnlineOutside: 11 1/4″ x 8 3/4″ x 6″Inside: 11″ x 8 1/2″ x 5 1/2″
Medium Flat Rate Box – 2 (side-loading)$13.75 Commercial Base$15.50 at Post Office & OnlineOutside: 14″ x 12″ x 3 1/2″Inside: 13 5/8″ x 11 7/8″ x 3 3/8″
Large Flat Rate Box$19.30 Commercial Base$21.90 at Post Office & OnlineOutside: 12 1/4″ x 12 1/4″ x 6″Inside: 12″ x 12″ x 5 1/2″

How Long is the Flat Rate Shipping Time?

Flat rate shipping utilizes Priority Mail and packages are usually delivered within 1-3 business days from when they are sent. The exact shipping time will depend on where the package is being sent from and its destination. There is also Priority Mail Express, which is typically 1-2 business days. 

Is Flat Rate Shipping Right for Your Ecommerce Store?

Flat rate shipping can provide a predictable shipping cost which can be a huge benefit for small businesses. It is not the best option for every ecommerce business, but can be a great solution for lower volume shippers handling their own packaging and running to the post office to ship orders.

It allows you to ship anything up to 70 pounds without worrying about calculating the shipping costs for each individual package. You can drop off packages at any USPS office for shipping. USPS flat rate shipping also includes delivery tracking and insurance up to $50 at no additional cost.


Flat rate shipping offers a great way to reduce the headaches that can come with shipping and makes it simple for you to ship your packages. You may even be able to pass savings on to customers.

However, USPS flat rate shipping is not for everyone. It is best used by retailers with low volume of packages and/or heavier items. It also does not work well for customers that want to save money on shipping and are willing to wait longer than 3 business days for a package.

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