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Everything you need to know about flat rate shipping

Flat rate shipping from USPS is a popular service used by many eCommerce sellers. Countless shapes, sizes, weights, and locations – one flat rate price. But is it everything it’s cracked up to be?

To help you decide if flat rate shipping is right for your online deliveries, we’re answering what it is, prices, benefits, considerations, and best use cases—all in one blog.

What is flat rate shipping?

Flat rate shipping is when you pay one rate for the entire shipping process. This includes packaging, carrying, tracking, insurance, and delivery.

Multiple carriers and fulfillment services (including Deliverr) offer flat rate services, but in this article we’re focusing on the USPS flat shipping service.

USPS Flat Rate delivers packages up to 70 lbs in weight, across the US within 1-3 business days, for a single flat fee.

How does flat rate shipping work?

There are four steps to flat rate shipping with the USPS:

1. Order your flat rate packaging

USPS offers eight different packaging options: three envelope sizes and five boxes. The packaging is free, and you can collect it from your local post office or have it sent to your business.

2. Pack your order into the box

Flat rate shipping prices are charged per the box’s size, meaning you don’t weigh packages or calculate shipping fees. As long as the package doesn’t exceed 70lb, you simply pack your order into the box.

3. Add the address

Whatever shipping method you use, it’s always good to adopt shipping label best practices. Add the customer’s address to the box in a clear and easily accessible place, alongside a return address should the package not arrive at its ultimate destination.

4. Buy your postage

Finally, purchase your flat shipping postage at a USPS post office or using an online postage provider.

You can post your package at your local Post Office or arrange a free package pickup.

What are flat rate shipping prices?

USPS links flat rate shipping prices to the size of the box used, as follows:

Flat rate packageDimensions (inches)Price at post officeCommercial base pricing
Flat Rate Envelope12 1/2 x 9 1/2$7.75$7.15
Legal Flat Rate Envelope9 1/2 x 15$8.05$7.45
Padded Flat Rate Envelope12 1/2 x 9 1/2$8.40$7.75
Small Flat Rate Box8 11/16 x 5 7/16 x 1 3/4$8.30$7.65
Medium Flat Rate Box (Top Loading)11 1/4 x 8 3/4 x 6$15.05$13.20
Medium Flat Rate Box (Sideloading)14 x 12 x 3 1/2$15.05$13.20
Large Flat Rate Box12 1/4 x 12 1/4 x 6$21.10$18.30
APO/FPO/DPO Large Box12 1/4 x 12 1/4 x 6$19.60$16.80


Are flat rate shipping prices cheaper than standard shipping prices?

Flat rate shipping prices can be lower than standard shipping prices, but they can be more expensive too, depending on what and where you’re shipping.

For example, a small box weighing 8lbs traveling from San Francisco to Denver costs:

  • $17.10 USPS Priority.
  • $8.30 USPS Flat Rate.

However, a large box weighing 5lbs, traveling within San Francisco costs:

  • $10.20 USPS Priority.
  • $21.10 USPS Flat Rate.

The general rule of thumb is flat cost delivery works best for small, heavy items traveling a longer distance. However other cost factors, such as packaging, insurance, tracking, and time savings, are also relevant.

It’s also good to remember that USPS Flat Rate isn’t the only flat fee shipping service available. At Deliverr, our all-inclusive fulfillment fees cover receiving, shipping, order handling, pick pack, and box costs – across standard, 3 Day, and 2 Day delivery.

The best way to find the most cost-effective option for your business is by using a fulfillment cost calculator to compare prices and services for your products.

What are the benefits of flat rate shipping?

The benefits of flat rate shipping for eCommerce sellers are numerous, including:


You don’t have to weigh packages or calculate shipping costs – simplifying your processes, increasing fulfillment efficiency, and helping you get orders out the door quickly.


The cost of flat rate shipping can reduce your shipping overheads, allowing you to deliver bigger, heavier, and longer-distance orders for a fraction of standard shipping costs. With flat rates, you can also charge customers the correct shipping price, rather than estimating postage and making up any shortfalls yourself.

Insurance and tracking

USPS flat rate shipping comes with tracking and insurance of up to $50 included. This benefits you and your customers, giving them the peace of mind they need to convert.


The USPS flat rate shipping services come with acceptable shipping speeds of three days or fewer across the US. This may expand your customer reach, increasing your sales without increasing your costs.


With one flat fee, you can encourage customers to spend more on your online store to make the most of the postage cost – a great upsell tactic.

What are the negatives of flat rate shipping?

Flat rate shipping isn’t the best option for all online sellers, with considerations including:


The USPS flat rate service delivers items within three days, which isn’t fast enough to qualify for fast shipping programs such as Walmart TwoDay. However, that doesn’t mean you can’t benefit from both flat rates and fast shipping programs.

For example, at Deliverr we provide flat rate fulfillment with shipping speeds eligible for fast shipping programs. Your customers get super-fast deliveries, while you benefit from all-inclusive pricing.


Flat rate deliveries aren’t always the most cost-effective option. We’ll cover this in more detail next, but you should shop around, because USPS might not be the best option for your profit margins.


USPS Flat Rate covers shipping only – you must complete all other fulfillment tasks. If you have an in-house fulfillment operation, this shouldn’t be a problem, but if you don’t have space or time to fulfill orders yourself, you need flat rate fulfillment instead of just shipping.

You should also note that USPS has restrictions on what products you can post, with alcohol, explosives, airbags, and similar products all prohibited.

Tip: Deliverr provides flat rate fulfillment – check your exact pricing by creating a free account.

Is flat rate shipping for me?

USPS flat rate delivery is an excellent service, but that doesn’t automatically make it the best service for your eCommerce business.

If you’re fulfilling orders in-house, and you’re happy doing so, USPS flat rate is a good choice for small and heavy items traveling some distance. You can also save on the post office prices by using an online postage provider to access commercial base rates.

If you’re interested in flat pricing but can’t or don’t want to handle fulfillment in-house, an all-inclusive fulfillment service is an excellent and cost-effective alternative. You access transparent, predictable, and competitive shipping fees while benefiting from someone else handling your fulfillment.

Relevant reading: When to shift from in-house to outsourced fulfillment

Alternatives to flat rate shipping

If flat rate shipping doesn’t float your boat, but you want to ensure your delivery charges cover your carrier costs, there are alternatives.

Dynamic checkout

Dynamic checkouts automatically calculate the shipping cost for customers when they input their delivery address. This covers your carrier costs, but note it can lead to cart abandonment once customers discover the total price.

Average shipping costs

By calculating your average shipping costs, you can provide customers with your own flat delivery fee, that covers your total costs over the year. However, be wary of excessively high shipping costs for small and lightweight items.


After learning about the benefits of single rate shipping, you might assume it’s a cost-effective shipping method for your eCommerce business. And for many, it is.

You can deliver US-wide without worrying about the weight or size of your packages – providing consistency and confidence.

However, the USPS’s flat shipping service isn’t always the only or best option for your eCommerce deliveries. Depending on the items you sell, where your customers live, and your fulfillment efficiencies, standard shipping services or an all-inclusive fulfillment service can be more cost-, time-, and growth-effective.

Which is the best option for you? Calculate to find out.

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