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Flat-Rate Shipping: What it is + When to Use It

Updated: Jul 25, 2023

Flat-Rate Shipping: What it is & When to use it

As an online seller, you’ll have definitely heard the term “flat-rate shipping”? But you may have found yourself wondering - what the heck is it? And how do I know when to use it instead of standard shipping?

Don’t worry. In this post, you’re going to receive a cover-all. By the end, you’ll know exactly what flat-rate shipping is, how much it costs, and when to use it (and when it’s best not to).


What is Flat-Rate Shipping?

With flat-rate shipping, carriers charge a fixed rate for shipping a package of a certain size. Weight (and distance traveled with USPS & UPS) does not impact shipping cost. This makes it easier for merchants to predict shipping costs vs. standard shipping. Plus, it offers them a way to save money when used correctly.

For example, sellers that ship small but heavy items like jeans can use flat-rate shipping to avoid weight-based costs.

And store owners shipping to USPS Zones further afield can reduce distance-based costs.

How Much Does Flat-Rate Shipping Cost in 2023?

The cost of flat-rate shipping is determined by the size of the box and prices are updated yearly by carriers. However, once they're set, they’re locked in for that year! Below, you’ll see the 2023 flat-rate prices for both USPS and UPS, as well as the various options for packaging. 👇

USPS Priority Mail Flat-Rate cost for 2023

Envelope / Box Type


Commercial Price

Price at Post Office & Online

Flat Rate Envelope

12 1/2″ x 9 1/2″



Small Flat Rate Envelope

10″ x 6″



Padded Flat Rate Envelope

12 1/2″ x 9 1/2″



Small Flat Rate Box

Out: 8 11/16″ x 5 7/16″ x 1 3/4″

Ins: 8 5/8″ x 5 3/8″ x 1 5/8″



Medium Flat Rate Box – 1 (Top-Loading)

Out: 11 1/4″ x 8 3/4″ x 6″

Ins: 11″ x 8 1/2″ x 5 1/2



Medium Flat Rate Box – 2 (Side-Loading)

Out: 14″ x 12″ x 3 1/2″

Ins: 13 5/8″ x 11 7/8″ x 3 3/8″



Large Flat Rate Boxes

Out: 12 1/4″ x 12 1/4″ x 6″

Ins: 12″ x 12″ x 5 1/2″



Max weight for packages: 70lbs.

UPS flat-rate shipping cost for 2023 (UPS Simple Rate)

You may notice UPS Simple Rate costing differs slightly to USPS flat-rate. While the price is still based on the size of the box, UPS allows you to select different level of service. And of course, the more expedited the service, the higher the cost.

The chart below shows rates for shipments between the 48 US states. However, you can view rates for Alaska and Hawaii here.

UPS Simple Rate Package Size

Cost via UPS Ground

​Cost via UPS 3 Day Select

​Cost via UPS 2nd Day Air

Cost via UPS Next Day Air Saver

Extra Small




















Extra large





Max weight for packages: 50lbs.

Pros of Flat-Rate Shipping

Beige flat-rate shipping boxes with beige tape.

Dodge peak season surcharges

The holiday season is a busy (and costly) time for shippers. But the great news is that most carriers don’t apply peak season surcharges when you use flat-rate shipping. So you can avoid surcharges and save money!

Get free packaging supplies!

When you use flat-rate shipping, you can pick up carrier boxes and envelopes for free! With USPS you can pick up from your local post office or order through the USPS website. As for UPS - you can order through The UPS Store online if you have an account, or pop into a physical store.

While free supplies sound great, there are some downsides. If you use USPS Priority Mail Flat-Rate, you can only use USPS branded supplies. That means you won’t be able to use your own packaging and provide a branded shipping experience for your buyers.

Predict shipping costs with ease

Standard shipping rates vary a lot because cost changes based on weight and distance traveled. Whereas flat-rates aren't affected by these factors. They’re fixed. As a result, it’s a lot easier to predict your shipping costs.

This is also great if you want to offer free shipping. Because you know you’re getting a steady rate, you can include the shipping cost in your product price. This then means that you can subsidize the cost of offering your customers free shipping.

Cons of Flat-Rate Shipping

Different dollar bill notes against white background to show that flat-rate shipping isn't always the most cost-effective choice.

It isn’t always the most cost-effective choice

Sometimes, standard shipping is more affordable. Therefore, if you go flat-rate all the time, you could actually be paying more than you need to.

How do you know if you’re getting the best rates? Well, shipping software like shows you the cheapest shipping options available in an instant. That way, you can be sure you’re never overpaying for shipping.

As an added bonus, eCommerce stores can access LARGE discounts with This includes up to 84% off USPS Retail and 78% off UPS Ground. As well as up to 73% off expedited air services like UPS 2nd Day Air® service and UPS Next Day Air®.

You have to use carrier packaging instead of branded boxes

The unboxing experience is a super important part of eCommerce. And beautiful, branded, custom packaging can make your brand memorable and delight your customer.

However, when you use services like USPS Priority Mail Flat-Rate, you have to use carrier packaging. Meaning that you’ll miss out on a key opportunity to connect your brand to your customer.

When Should I Use Flat-Rate Shipping (And When Should I Not)?

Mixed-race woman holding white and brown flat-rate shipping boxes.

Usually, it’s best to use flat-rate shipping if your store ships small, heavy items, and if you regularly ship longer distances. This is because weight (and distance traveled with UPS & USPS) doesn’t affect flat shipping rates. So you can avoid cost increases for packages that are heavier and travel further (i.e. to a shipping zone with a higher number).

For example, if you’re sending packages between 1-20lb long distance, it’s normally best to use a flat-rate box. And for items over 20lbs, flat rate boxes are also generally the ideal choice.

That being said, there’s also a time NOT to use flat-rate shipping…

If an order falls quite a bit under the weight and dimensions of a flat-rate box, standard shipping will probably be more cost-effective. By using a flat-rate box that’s not right for your product, you’ll end up paying for extra space you don’t need. Plus, if you’re only shipping locally, flat-rate might end up being more expensive.

And if you’re mailing a product under 1lb like light jewelry or a t-shirt, flat-rate packaging probably won’t be the best option.


There you have it. Now you know what flat-rate shipping is and when to use it. Let’s recap on our 3 main takeaways... 👇

  • Flat-rate shipping is when carriers charge a set rate for mailing a package of a predetermined size. Your shipment's weight (and distance traveled with USPS & UPS) has no impact on the shipping cost.

  • It’s best to use flat-rate shipping when your store ships small, heavy items, or if you regularly ship longer distances. In these instances, you’ll save money on shipping when using flat-rate options.

  • While flat-rate shipping makes it easier to predict shipping costs and may be cheaper in some contexts, it’s not ALWAYS the best option. Sometimes, standard shipping is more cost-effective. To make sure you’re getting the best rates each time, use shipping software like


How long does flat-rate shipping take?

If you’re shipping USPS Priority Mail Flat-Rate, it usually takes 1-3 business days to deliver. Whereas with UPS flat-rate options (UPS One Rate), delivery times vary depending on the service you choose. Often, delivery will be within 1-5 days, and will be quicker if you choose an expedited air service.

If your small business ships with UPS, they also apply their money back guarantee to UPS Simple Rate. Therefore, if your package doesn’t arrive on time, you’ll receive a refund!

Is flat-rate shipping cheaper?

Not always. If you're mailing small, heavy items or shipping longer distances a lot, flat-rate shipping is usually cheaper. However, when you're mailing locally or sending lightweight items, standard shipping options can be more affordable.


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