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Jaidyn Farar

What Is Flat-Rate Shipping and How To Use It to Your Advantage

by Jaidyn Farar

Shipping costs can be hard to predict, and it’s no wonder. Lots of variables come into play: Product size and weight, target delivery time, origin and destination, and extra surcharges for fuel, residential delivery, or peak season.

Flat-rate shipping eliminates many of these variables. It simplifies the shipping process for businesses by helping them predict costs more accurately and spend less time measuring product dimensions and weight. 

What is flat-rate shipping? How does it work? And how does it stack up next to standard shipping? This article will explain what sets flat-rate shipping apart and how to know if your company should use it.

Note: Wanting to compare flat-rate shipping costs for the major carriers? Skip down to the section “Flat-rate shipping with USPS, UPS, and FedEx.”

What is flat-rate shipping?

Flat-rate shipping is a shipping method where the rate is based on a box or envelope’s size rather than the dimensional (DIM) weight of the object being shipped. As long as you don’t exceed the maximum weight of the flat-rate box, you can ship any product for the same price. 

Flat-rate shipping simplifies the shipping process, eliminating the need to weigh and measure products to determine the cost to ship them. It comes with additional benefits too—for example, it’s usually exempt from surcharges. And if you ship with USPS or UPS, the price is the same regardless of the package’s destination (FedEx takes shipping zones into account). While flat-rate shipping is a great option for dense, heavy items, it may not be cost-effective for lightweight items. 

What is the difference between standard and flat-rate shipping?

Unlike flat-rate shipping, standard shipping takes into account a package’s DIM weight—a combination of its weight, dimensions, and a carrier-specific dimensional factor—and the distance it’s traveling. 

Standard shipping costs are harder to predict, but it can be a more affordable method than flat-rate shipping. In fact, standard shipping is usually the cheapest way to ship products. It does come with downsides, though: Not only do you have to spend more time determining each order’s weight and size, but you also face longer delivery times.

How does flat-rate shipping work?

When using flat-rate shipping, you can choose from various flat-rate boxes or envelopes, each with different dimensions and volumes. Larger boxes cost more to ship, and regardless of the packaging size you choose, there’s always a weight limit. 

Getting started with flat-rate shipping is simple—just follow these steps:

1. Choose your carrier

First, decide which carrier you’ll be using. UPS, USPS, and FedEx all offer flat-rate shipping options, which you can learn more about below. If you’re interested in saving money with a multi-carrier shipping strategy, use shipping software like EasyPost or EasyPost Enterprise to automate carrier selection and find the best rate for each shipment.

2. Select the box size you need

Next, choose the correct box size (if you’re sending non-breakable products, you can also use a padded mailer or envelope). For the best value, make sure to select the smallest package your product can fit in. 

USPS and FedEx both require you to use their flat-rate packaging, while UPS lets you source your own boxes and envelopes.

3. Pack the box, print a shipping label, and arrange for carrier pickup

From there, proceed as usual. Pack the box and print a shipping label, then simply drop your shipment off with the carrier or schedule a pickup. With that, your flat-rate package is on its way to the recipient!

How long does flat-rate shipping take? 

Flat-rate shipping times vary by carrier, but you can generally expect delivery to take between one and five days. UPS offers multiple delivery time options: five days, three days, two days, and next-day delivery. USPS flat-rate shipments take between one and three business days. FedEx only offers flat rates for its express services, so you can choose between three-day, two-day, and next-day delivery. 

Advantages of flat-rate shipping

Why use flat-rate shipping? Its advantages include speed, cost savings, and predictability. 

  • Fast delivery. Flat-rate deliveries generally take just a few days to complete.
  • Lower shipping costs. If you’re shipping small, heavy items, flat-rate shipping is the way to go. Because you’re not paying more for the additional weight, you save money compared to other shipping methods.
  • Lower packaging costs. USPS and FedEx both provide free flat-rate packaging, which helps you save money on materials.
  • No peak season surcharges. Since flat-rate shipping is usually exempt from surcharges, you don’t need to factor them into your shipping cost forecasts.
  • Predictable rates. Flat-rate shipping offers a predetermined rate for packages of a certain size, making it easy to understand and predict shipping costs. 

Disadvantages of flat-rate shipping

Flat-rate shipping isn’t right in every situation. Let’s look at a few potential disadvantages.

  • You risk overpaying. In some cases, flat-rate shipping may be more expensive for customers, especially if they live nearby or order lightweight items.
  • It’s not always practical. Some products are significantly larger or heavier than the average, making flat-rate shipping less practical. 
  • You can’t use branded packaging. If you decide to go with USPS or FedEx, you’ll need to use their flat-rate packaging. For some businesses, this isn’t a big deal, but it could be a lost opportunity if you prefer to have custom-branded packaging. 

Flat-rate shipping with USPS, UPS, and FedEx

As mentioned above, USPS, UPS, and FedEx all offer flat-rate shipping options. USPS and FedEx offer a variety of flat-rate box sizes, while UPS lets you use your own packaging. To help you compare box sizes and prices, we’ve compiled some key information into the tables below. (The rates are accurate as of January 2024.)

USPS flat-rate shipping

USPS flat-rate packages ship anywhere in the United States, and the maximum weight is 70 pounds. 

Package type
Flat Rate Envelope
$8.05 Commercial Pricing$9.65 at Post Office
12 1/2″ x 9 1/2″
Window Flat Rate Envelope
$8.05 Commercial Pricing$9.65 at Post Office
10″ x 5″12 1/2″ x 9 1/2″
Small Flat Rate Envelope
$8.05 Commercial Pricing$9.65 at Post Office
10″ x 6″
Padded Flat Rate Envelope
$8.80 Commercial Pricing$10.40 at Post Office
12 1/2″ x 9 1/2″
Legal Flat Rate Envelope
$8.35 Commercial Pricing$9.95 at Post Office
15″ x 9 1/2″
Small Flat Rate Box
$8.55 Commercial Pricing$10.20 at Post Office
Outside: 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 (Top-Loading)
$14.75 Commercial Pricing$17.10 at Post Office
Outside: 11 1/4″ x 8 3/4″ x 6″Inside: 11″ x 8 1/2″ x 5 1/2″
Medium Flat Rate Box (Side-Loading)
$14.75 Commercial Pricing$17.10 at Post Office
Outside: 14″ x 12″ x 3 1/2″Inside: 13 5/8″ x 11 7/8″ x 3 3/8″
Large Flat Rate Box
$19.90 Commercial Pricing$22.80 at Post Office
Outside: 12 1/4″ x 12 1/4″ x 6″Inside: 12″ x 12″ x 5 1/2″
APO/FPO/DPO Flat Rate Box
$18.35 Commercial Pricing$21.20 at Post Office
Outside: 12 1/4″ x 12 1/4″ x 6″Inside: 12″ x 12″ x 5 1/2″

Note that UPS Commercial Pricing, as well as discounted rates for FedEx and UPS, are available through the EasyPost Shipping API.

UPS flat-rate shipping

UPS Simple Rate includes five box sizes. Prices vary based on the service you use, with longer delivery times costing less. The information below applies to shipments between the 48 contiguous states.

When shipping flat rate with UPS, you use your own boxes. Instead of calculating price by dimensions, you’ll calculate by cubic inches. Just multiply the length, width, and height to determine your package’s size in cubic inches.

UPS flat-rate packages have a weight limit of 50 pounds.

Package type
Volume (cubic inches)
Extra Small
Extra Large

Learn more about UPS flat rate shipping.

FedEx flat-rate shipping

FedEx One Rate shipping varies based on zone; local zones (destinations between 0 and 150 miles from the origin) are the most affordable, while regional and national zones are the most expensive.

The rates below are ranges for three-day shipping (FedEx Express Saver®) across local and national zones. To see rates for other services, see the pricing chart here.

FedEx flat-rate shipments have a weight limit of 50 pounds.

Maximum volume (cubic inches)
FedEx® Envelope
9-1/2" x 12-1/2"Reusable Envelope:9-1/2" x 15-1/2"Padded Envelope:9-3/4” x 11-1/2”
FedEx® Pak
10-1/4" x 12-3/4",12" x 15-1/2"Padded: 11-3/4" x 14-3/4"Reusable Sturdy Pak: 10" x 14‑1/2"
FedEx® Small Box
10-7/8" x 1-1/2" x 12-3/8"8-3/4" x 2-5/8" x 11-1/4"
FedEx® Medium Box
11-1/2" x 2-3/8" x 13-1/4"8-3/4" x 4-3/8" x 11-1/4"
FedEx® Large Box
12-3/8" x 3" x 17-1/2"8-3/4" x 7-3/4" x 11-1/4"
FedEx® Extra Large Box
11-7/8" x 10-3/4" x 11"15-3/4" x 14-1/8" x 6"
FedEx® Tube
6" x 6" x 38" 

When to use flat-rate shipping

If your business meets one or more of the qualifications below, consider looking into flat-rate shipping. 

  • You ship small, heavy items. Flat-rate shipping works well for these products because it’s affordable and predictable, letting you set transparent shipping prices for your customers.
  • You handle fulfillment in-house. If you take care of logistics in-house, flat-rate shipping allows for easier cost calculation and budgeting.
  • You ship across zones from a central location. Since many flat-rate offerings are the same regardless of distance, it’s a great option if you ship from a single, centrally-located distribution center.

When not to use flat-rate shipping

Maybe flat-rate shipping isn’t right for your business at the moment. Read through the list below to see if it’s not a great fit.

  • You want more control over the shipping experience. If customization and flexibility are crucial for your business, be aware that flat-rate shipping might limit your options.
  • You’re shipping lightweight products. Variable rates based on weight often offer better value for lightweight items. 
  • Only shipping to a certain area. If your business has a localized customer base, using flat-rate shipping may not be necessary.

Streamline your ecommerce shipping with EasyPost

Flat-rate shipping minimizes differences in shipping rates due to DIM weight, distance, and surcharges. If you use it strategically, you can save big on shipping—and pass those savings on to your customers. But why stop there? With EasyPost, you can access even better rates, save time with automatic label generation, and more. 

EasyPost provides solutions for both small and medium-sized businesses and enterprises. To get started, sign up for free or talk to a shipping expert