USPS Flat Rate Shipping: Meaning, Advantages, Shipping Charges

April 25, 2024 A United States Postal Service (USPS) shipping van.

Are you wanting to optimize cost-efficiency for your e-commerce business and expedite your shipping process?

Look no further than USPS flat rate shipping service. 

Shipping margins play a crucial role in the profitability and long-term viability of ecommerce businesses.

No matter the size or weight of your shipment, with flat rate shipping service, the cost won’t be affected.

You will save money if you send large things using this method. However, for lightweight packages, it won’t be that much convenient. 

Is Flat Rate Shipping service the Perfect Match for Your Ecommerce Business?

Don’t worry! We are here to help you. 

This article will give you all kinds of information like what is flat rate shipping, what are the restrictions and what are the shipping charges. 

What is flat-rate shipping?

Flat rate shipping is a service where shipping charges are calculated by box size rather than its dimensional weight. 

It means the shipping rate is fixed for all kinds of boxes. no matter what is the size or dimension of the product, the shipping charges will be the same. 

You can send any weight at the same price until you reach the maximum weight. 

The actual answer to what is flat rate shipping is it is a service that reduces your shipping charges and saves you money.

However, the charges depend on the freight carriers, as each carrier has different prices. 

USPS Flat Rate Shipping Service: How does it work?

The USPS Flat Rate shipping service offers the convenience of shipping your package to any location within the United States in 1-3 business days, all for a fixed fee. To utilize this service, simply follow these steps:

  • Order USPS flat rate box sizes at no cost. It is important to use the designated Flat Rate boxes in order to benefit from the standardized shipping rate. These boxes can be ordered online or acquired at your local Post Office.
  • Register for a free AMZ prep account to access the most affordable rates for USPS Flat Rate shipping service. Additionally, you can conveniently generate shipping labels from the comfort of your office or home through this account.

Bonus tip! Assess whether a USPS Flat Rate box sizes present the most cost-effective option for the specific items you intend to ship, as it may not always be the most economical choice.

Benefits of Using Flat rate shipping service:

If you are running a small business and want to save huge shipping charges, Flat rate shipping service is the best option. There are lots of benefits or advantages of using this service, such as:

Not to worry about weight:

When you ship your product through flat rate service, you don’t have to check weight and dimensions. Using flat rate shipping service rather than standard shipping regarding heavy-weight inventory is better. No matter the weight of your product, it costs the same.  

Note: flat rate shipping service is not available in all the states. It is only available in the US and Canada. But you can ship any product under 70 LBS across the United States or to approved international shipping. 

Shipping insurance:

You will get insurance up to $50 for every flat rate shipping in us. It is worth it and depends on shipping value and volume. However, it is more convenient for high-volume items than low-volume shipments. 


 When you ship your products through a flat rate service, you give the buyers a fixed price, which clarifies the selling mechanism. 

As a result, they trust you and relate better towards your product. They prefer your products to other sellers as they don’t have to pay extra handling or shipping fees. 

Simplified management: 

In standard shipping service, your e-commerce website needs a shipping calculator, but in flat rate shipping time, you don’t need any calculator. 

You don’t need to modify the shipping cost for each good based on dimensions and weight. It gives more elasticity to focus on fulfilment operations, including sourcing, packaging, etc. 

Less shipping cost:

This process does not incur any additional costs for the customer. This way, they don’t have to worry about shipping and focus more on buying the product.

 When you choose shipping companies like AMZ Prep, you can optimize your shipping costs by opting for flat-rate inter-territory shipping.

Time Management:

It’s hard to offer time to action other than your core business. For this reason, many companies hesitate to contact different shipping corporations and finally set the shipping charges.

 Standard shipping charges take time as freight carriers calculate rates based on weight, dimensions and time zones.

The packages have already operated on dimensions and weight. This streamlines the process and accurately manages flat rate shipping time.

Easy steps to ship your flat rate box:

Flat rate shipping meaning or means the shipping charge is not dependent on the product’s size, shape or weight; hence the word comes from “flat rate.” All major freight carriers offer this service, and each company has restrictions. Here we discussed those easy steps to ship your products through shipping flat rate services.

  • Select your shipping carrier:

First, you have to choose a shipping carrier that is more convenient for you according to your needs and location. 

  • Ensure the box meets the size requirements:

After selecting the carrier, decide which box or envelope meets your size requirements. 

Pack your products:

Pack your products and add the address in the package to the customer.

Ship your products: 

The last step is to include a shipping label and then drop off the shipment at the shipping center, like the post office. 

Flat rate shipping Charges:

Many shipping companies offer flat rates and boxes to avoid confusion regarding sizes, dimensions, and shipping.

The charges of flat rate shipping service depend on the USPS flat rate box sizes and the shipping carriers. 

USPS shipping rate:

Flat rate boxes

Post office price

Commercial price


One rate envelope



12 1/2″ x 9 1/2″

Small box



8 11/16″ x 5 7/16″ x 1 3/4″

Medium box – 1



11 1/4″ x 8 3/4″ x 6″

Medium box- 2



14″ x 12″ x 3 1/2″

Large box



12 1/4″ x 12 1/4″ x 6″

UPS shipping rate:

Flat rate boxes

Shipping price

Dimensions (cubic inch)

Extra small box



Small box



Medium box



Large box



Extra Large box



FedEx shipping rate:

Flat rate boxes

Shipping price


One rate envelope


9-1/2″ x 12-1/2″

Small box


10-7/8″ x 1-1/2″ x 12-3/8″

Medium box


11-1/2″ x 2-3/8″ x 13-1/4″

Large box


12-3/8″ x 3″ x 17-1/2″

Extra Large box


11-7/8″ x 10-3/4″ x 11″

Restrictions you should maintain while shipping:

When you ship your products through a flat rate service carrier, you should maintain a guideline such as:

Prohibited Materials:

Prescription medications, guns, and alcohol are prohibited and shipped by only manufacturers and dealers following superior rules.

You generally can’t ship tobacco products. However, you can ship cigarettes with few exceptions. 

Priority mail restrictions:

You cannot send anything; there are some restrictions. When it comes to usps flat rate boxes, you cannot include

  • Explosives
  • Airbags
  • Gasoline
  • Firearm ammunition
  • Alcohol and more
  • Weight of products more than 70 pounds

Express mail shipments:

Express mail shipments are best for overnight delivery and sensitive documents or items. You cannot ship products over 70 pounds. You can send your products everywhere in the US, including military addresses and post offices.

International shipments:

When you deliver an international shipment, it takes 3 to 10 days. You have to maintain one of the boxes. Due to international restrictions and prohibitions, you cannot deliver more than 20 pounds of products. 

Contents need to fit:

The package contents must fit inside the envelope or mailing box you select.  

Best freight carriers who offer flat rate services:

Three shipping carriers offer flat rates, such as USPS, UPS, and FedEx

This image depicts a list of top flat-rate shipping carriers

USPS Flat Rate:

The US postal service (USPS) offers flat rate shipping service with their priority mail express and priority mail services.

USPS sets some restrictions on shipping your products.They fix their rates based on package size.

Shipping and weight do not matter in pricing.You cannot ship products of more than 70 pounds.

UPS Flat Rate:

UPS offers you to utilize your mailing envelope or box and still gain the advantages of a flat shipping rate.

Your shipment should be under 50 pounds.Shipping size should not be more than 1728 cubic inches.

In UPS flat rate, you will use your packaging.Thus it would be best if you did some math to calculate the rate category.

The rate differs for several states in the US, it has one rate, and for Hawaii and Alaska, the rate is a little bit higher. 

FedEx Flat Rate:

FedEx is one of the best Flat Rate shipping services with different rates.

The charges depend on the service and size of the package.You can use their packaging to obtain an advantage of their one-rate program.

FedEx charges according to distance; if the distance is high, the charges will also be high.

You can ship envelopes not more than 10 pounds and tubes and boxes not more than 50 pounds.

Disadvantages of using Flat rate shipping:

Everything has its advantages as well as disadvantages. Such as;

Spend money on unnecessary things:

Shipping flat rate is more useful when your shipment size is large and you will deliver the shipment to a longer distance.

It won’t be that beneficial if you want to deliver your products over a shorter distance. 

Lost brand value:

They promote their own company when you deliver your shipment through a big shipping company.

Thus your branding value will not be considered. 

Unable to create the best customer satisfaction:

Flat-rate shipping may be more beneficial for merchants, but that does not mean it will also benefit customers. Sometimes it takes longer to deliver products which is not a good sign for customer satisfaction. 

Difference between Standard rate and flat rate shipping:

Standard rate and flat rate services are pricing policies for shipping orders.

You can offer buyers a flat shipping rate for each specific region or specific weight or a premium shipping rate that can differ even within a region and is determined by various factors.

With the flat rate, you can send every item for the same rate, typically within zones.

In most situations, this rate is calculated by the e-commerce site itself, according to their delivery partner.The flat-rate service is based on different shipping locations.

For example, a flat shipping rate may vary depending on the zone and location to which the item will be delivered.

Best time to consider a flat rate shipping service:

Let’s check when you should consider a flat-rate service;

If you are dealing with small and heavy items: Flat rate service saves you the additional cost of shipping packages with a large DIM weight

If you are utilizing your self-fulfilment service: Brands that practice self-fulfilment is aided by ship flat rate because company-supplied packaging and consistent pricing lower handling costs and streamline the packaging process. 

If you are using centralized fulfilment strategies: If you take a nationwide warehouse that delivers your orders, flat rate shipping saves you the additional cost of crossing multiple shipping zones. 

Recommended Read:
Amazon Warehouse Deals: Your Guide to Unlock Savings

Factors affecting shipping flat rate services:

Flat rate service is only beneficial when you have constant or regular deliveries. Some factors determine your shipping rate. 


So if the shipment is set to 50 pounds.So any box or package under this weight is qualified for the flat rate.

Normally most shipping carriers set the range at 70 pounds.

Therefore, all items under this are eligible for a one-rate shipping service.

Time zone:

Time zones play a vital role in deciding whether flat-rate shipping is right for you.

The closer it’s to your starting point, the lower the prices.Shipping will be more expensive if you ship out of the time zone.

That’s why you should have clarity that you have several customers from one time zone.

Having more orders and customers in a similar time zone is an advantage for you. 


Most shipping carriers have specific sizes for each package type: large, medium and small.

This also makes shipments consistent to load, stack and unload.

They even have bins with specific dimensions.Flat-rate shipping is only possible in certain sizes or dimensions.

This allows e-commerce businesses to bring their packages and use these containers.

For example, sets of books, clothes, tiny metal objects, papers, etc., that easily fit in boxes of a certain size.

How AMZ Prep helps you to ship your products:

Optimizing shipping is another way to reduce costs and increase margins if you face difficulties shipping your products and investing lots of money in shipping.

AMZPrep is a 3PL that ships your products to several fulfilment centres.

Here is how AMZ Prep helps you to ship your products;

Monitor the whole fulfilment process:

With AMZPrep, your shipping will get easier as they monitor the entire fulfillment process from labelling to delivering the product to the customer.

That means you can manage inventory as well as monitor the entire fulfillment procedure from start to last.

Store inventory:

You can also store your inventory in their warehouses, bringing your items closer to customers to reduce transit times and shipping costs.

Automatic fulfilled orders:

After placing an order, it automatically updated to the fulfilment centre. After that, it was picked, labelled and shipped.

Provide tracking info to the customers:

After shipping the products, customers will get tracking information for their orders to check their products’ status.


Flat-rate shipping is one of the most simplified and uncomplicated ways of shipping.Here, you will get fixed rates for every type of weight and box. Unlike other shipping methods, shipping rates are determined by the type of item, size, time zone and dimensions. Also, it’s one of the most beneficial options for merchants with multiple orders and constant deliveries. 


Questions About Flat Rate Shipping

Does Flat rate services value money?

If you are shipping a high dimension and heavy product, then a Flat rate shipping service will be beneficial for you. But if you are shipping a lighter and big size product, it will be better to ship with a regular shipping service.
It’s important to research and compare different service providers to determine which pricing model and provider will provide the best value for money for your specific needs.

How much is USPS shipping?

The cost of USPS shipping depends on several factors, including the weight of the package, the dimensions of the package, the distance it needs to travel, and the shipping service selected.
When you choose flat rate shipping over standard shipping, your overall shipping cost reduces. so you will gain more profit margins.

Is shipping flat rate cheaper?

In some cases, shipping with a flat rate can be cheaper if the package is heavy and going a long distance, but in other cases, it may be more cost-effective to use a regular shipping option based on the package’s weight and destination.
 It’s important to compare shipping rates from different carriers and consider the package’s specific requirements to determine the most cost-effective shipping method.
 However, the best part is it makes it easier to budget the shipping costs.
In some cases, shipping with a flat rate can be cheaper if the package is heavy and going a long distance, but in other cases, it may be more cost-effective to use a regular shipping option based on the package’s weight and destination.
 It’s important to compare shipping rates from different carriers and consider the package’s specific requirements to determine the most cost-effective shipping method.
However, the best part is it makes it easier to budget the shipping costs.
Please send us a message on our contact-us page to learn more.

How long does flat-rate shipping take?

The delivery time for flat-rate shipping depends on the shipping carrier and the destination of the package. 
It usually takes 2 to 3 business days to deliver the products during the non-peak season.
Generally, flat-rate shipping takes between 1 to 3 business days for domestic shipments, and between 6 to 10 business days for international shipments.

Can I offer flat rate shipping for international orders?

Flat rate shipping is only available for the US and Canadian people. And in this service you can ship any products up to 70 lbs within the preferred dimension. however, you can ship any small size product to any large international shipping. 
Additionally, it’s a good idea to clearly communicate any restrictions or limitations on your flat rate shipping offer, such as excluded countries or order values, to avoid any confusion or issues with customers.

Can I choose different flat rate options for different products?

Yes, you can charge separately for every different product. The charge is multiplied by the amount of items in your cart.

This can be useful if you have products that vary in size, weight, or destination, and therefore have different shipping costs.

This will allow customers to see the appropriate shipping rate based on the product they are purchasing, and can help ensure that you are covering your shipping costs while providing a fair and transparent pricing structure for your customers.

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