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What you need to know about USPS flat rate shipping


by Jules

On 2018 M11 7

by Jules

As an eCommerce store owner, you've probably been looking for affordable and convenient shipping options. We're going to go out on a limb and say that you've come across flat rate shipping as an option, and that it may sound appealing for your business.

You might have read that this shipping option saves a lot of money, but before you take that leap, it's best to understand what this shipping option is all about.

In this post, we'll discuss what flat rate shipping means and the variety of services that the United States Postal Service (USPS) offers if you're interested in moving forward with this option.

What is flat rate shipping?

Flat rate shipping is a shipping service that you can find offered by a variety of couriers, notably USPS. It's major feature is that it charges one rate regardless of the weight of the package.

If you're shipping very heavy items and it happens to be able to fit within the various packaging options provided, this could potentially save you money on shipping costs.

How does flat rate shipping work?

USPS offers different box sizes and envelope types, all with different pricing. As long as your item fits within the packaging and it is below the weight limit, you only have to pay that specified price - making the calculation of your flat rate shipping costs easier.

Packaging your shipments

Many businesses like using USPS' flat rate service because the boxes and envelopes are provided free of charge. Also worth noting is that the shipping label must match the box you already have.

Apart from being under the weight limit, it is also important that the content of a given box or envelope fits inside properly, without requiring any modifications to the packaging, such as altering the folds.


There are definitely restrictions on what items can be shipped. You can't ship ammunition, gasoline, airbags, explosives, cigarettes, marijuana, and any other form of tobacco in flat rate boxes.

For flat rate shipping domestically within the US, the maximum weight approved for each package or envelope is 70 lbs.

For USPS international flat rates, the maximum weight for Priority Mail International Flat Rate Envelopes and Small Flat Rate Priced Boxes is 4 lbs. Additionally, the maximum weight for medium and large Priority Mail International Flat Rate Boxes is 20 lbs.

It's also worth noting that some countries have lower weight restrictions.

Where you can ship to

With domestic flat rate boxes, you can ship packages to any location within the United States.

For international shipping, you can ship to more than 190 countries. For a complete list, visit USPS' Index of Countries and Localities for more information and potential restrictions for your destination country.

Delivery timeframe

For domestic service, the delivery timeframe is usually between 1 to 3 business days.

With the USPS international flat rate service, the delivery timeframe is quoted as 6 to 10 business days.

Available boxes and prices

Popular USPS flat rate box sizes include:

Using flat rates for eCommerce

While the free supplies and pricing relative to weight may make flat rate shipping seem alluring, it may not be the best solution for the following reasons:

  • They don't provide a lot of information. How did they calculate the rate? It also doesn't provide adequate information on duties and taxes, making it difficult for overseas customers to determine if additional fees could be added.

  • Figuring out the break-even point can be complicated. To determine whether you're actually saving money on shipping, you need to calculate the break-even point. This requires a very complicated comparison of your business' package volumes, weights, and distances.

Here are additional reasons why you should avoid flat rate shipping.


While flat rate shipping sounds good in theory, you'll really need to analyze your business' shipping needs and costs to decide whether it's really a good deal for you.

In most cases, it's best to provide calculated rates at checkout for all customers so they pay the exact shipping costs - allowing you to avoid overpaying for shipping in the first place.

For more information about how to offer this option for your store, install our Rates at Checkout feature – it's free!