Your Guide to USPS Small Flat Rate Boxes

USPS Flat Rate is the secret saver for heavy packages. Ship a gold brick or a feather – the price is the same. With Flat Rate, you’re not paying for shipping by weight or distance like typical services. You only pay a single fixed price.

So what are your options for small USPS Flat Rate boxes? Well, a Flat Rate box lets you send any item weighing less than 70 pounds anywhere. The only restriction is that your item must fit the box.

If you’re like most shippers, you want your box to fit your item perfectly. With this in mind, today we highlight your options for USPS small Flat Rate boxes.

Don’t forget: you can save up to 91% off all Flat Rate shipping with Easyship. To see exactly how much, try our free shipping rate calculator. Just enter your package weight and destination for an instant savings quote.

The Cost of USPS Small Flat Rate Boxes

To use USPS Priority Flat Rate services, you’ll need to ship in a Flat Rate box. For best results, try to fit the box to your item. Not because using a bigger box will raise the price – hey, this is the Flat Rate we’re talking about – but because it looks better on the receiving end.

You can choose from a handful of boxes at a Flat Rate. Here they are listed from smallest to largest:

What is USPS Priority Mail Flat Rate?

USPS Priority Mail Flat Rate is a cost-effective shipping service that lets you send packages under a maximum weight of 70 pounds for a flat rate, regardless of distance, dimensions, or weight. 

Instead of calculating shipping prices based on volume, shape, or delivery zone, flat rate pricing simplifies your shipping experience. 

Packages sent via Priority Mail Flat Rate typically arrive within 1-3 business days, making it a fast, reliable choice for businesses, eBay sellers, and everyday customers.

To use this service, you must ship with USPS Flat Rate boxes or a flat rate envelope, which are available in standard sizes and can be ordered online or picked up at your local post office. 

These specially marked containers—including the popular USPS Small Flat Rate Box (e.g., 8 5/8 x 5 7/16 x 1 5/8″)—serve as prepaid postage and eliminate the need for your own packaging or weighing. Just pack, label, and ship—it’s that simple.

Here are several reasons why Priority Mail Flat Rate is a smart choice over other postal service or courier options like UPS or FedEx:

Economical for heavy items

The flat rate system is often the cheapest option for shipping heavy items over long distances. Since the price remains fixed for packages under the maximum weight, it’s a great way to save on shipping—especially for businesses taking advantage of commercial rates or discounted rates.

Convenient and easy to use

With flat rate shipping, there’s no need to measure cubic inches or use your own box. As long as your item fits within the normal folds and closed container flaps of the flat rate box, and adheres to specific regulations, it’s ready to go. This ease makes it ideal for commercial, retail, and office use.

Fast delivery

Priority Mail shipments via flat rate usually arrive within 1–3 business days, offering quick service without the uncertainty of variable delivery times or costs.

Free and easy access to shipping supplies

You can order USPS flat rate boxes and envelopes, including 12 x, 4 x, and 2 x sizes, directly online or pick them up at your post office—free of charge. This helps streamline shipping without the added purchase cost of supplies.

No hidden fees

USPS Priority Mail Flat Rate avoids extra charges for fuel, rural delivery, or volume pricing, making it more transparent than many alternatives. With easy label creation and tracking, you can print, file, and monitor your shipment without surprises.

Note: USPS has restrictions on mailing certain items such as hazardous materials, smokeless tobacco, or anything that doesn’t fit using normal folds or closed container flaps. Always check USPS guidelines for full details.

How to Ship a Small USPS Flat Rate Box

Shipping small USPS Flat Rate boxes is straightforward. Here’s how it’s done:

1. Get a small USPS Priority Mail Flat Rate box: Order these online for free at USPS.com or use them when you drop into your local Post Office. The bigger the box, the higher the price (as shown above).

2. Pack your items and seal your box: Any item that weighs less than 70 pounds can be shipped Flat Rate, so long as it fits inside the box.

3. Ship it: Bring your Flat Rate box to any Post Office or arrange for pickup. Flat Rate envelopes can also be dropped in USPS blue boxes.

Small Flat Rate Boxes from FedEx and UPS

Both UPS and FedEx offer flat rate shipping services. Just like USPS Priority Mail Flat Rate, UPS Simple Rate and FedEx One Rate come with box-use requirements. Be sure to read up on these services before you dive in.

Here’s a quick overview of shipping boxes and prices for UPS and FedEx flat-rate services.

UPS Simple Rate Small Boxes

UPS Simple Rate small boxes come in two sizes:

UPS Simple Rate Extra Small Box

• Maximum Size: 1-100 cubic inches
• Sized for: Sunglasses or a ceramic mug
• Price: From $9.45

UPS Simple Rate Small Box

• Maximum Size: 101-250 cubic inches
• Sized for: A hardcover book or tissue box
• Price: From $12.40

Read our full guide to UPS Simple Rate to learn more.

FedEx One Rate Small Box

The small FedEx One Rate box lets you ship items that weigh 50 pounds or less to anywhere in the US for a fixed price.

• Dimensions: 10-7/8 x 1-1/2 x 12-3/8"
• Sized for: Books and magazines
• Price: From $16.75

Read our full guide to FedEx One Rate to learn more.

USPS Small Flat Rate Boxes with Easyship

USPS Small Flat Rate boxes let you ship small items of 70 pounds or less to anywhere in the US for a flat fee. USPS Small Flat Rate box prices are just $8.45. Or you may prefer to use a flat rate with UPS or FedEx instead.

Not saving money with Easyship yet? Easyship is 100% free to use for merchants shipping up to 100 packages per month, including Flat Rate shipping. You save up to 91% off instantly. There’s nothing to lose.

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USPS Small Flat Rate Boxes FAQ

Can small flat rate boxes go in a mailbox?

Yes, small flat rate boxes can fit inside a mailbox depending on the size of your mailbox.

Is the small flat rate box big enough to fit an 8-inch tablet with charger and original box?

Yes, a small flat rate box can fit an 8-inch tablet with a charger in an original box.

What are the dimensions of a USPS Small Flat Rate Box?

The box measures 8 5/8" x 5 3/8" x 1 5/8".

How much does it cost to ship a USPS Small Flat Rate Box?

The cost is a flat rate (currently around $10.40 retail, or lower with commercial/Easyship discounts), no matter the weight up to 70 lbs.

What is the weight limit for a USPS Small Flat Rate Box?

The maximum weight allowed is 70 pounds.

Can I track a USPS Small Flat Rate Box?

Yes, tracking is automatically included with every flat rate shipment.

Can I ship internationally with a USPS Small Flat Rate Box?

Yes, USPS offers Priority Mail International Small Flat Rate Boxes for worldwide delivery, with customs forms required.