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Your Guide to USPS Small Flat Rate Boxes

You can ship a lot for a little in USPS Flat Rate boxes.
Your Guide to USPS Small Flat Rate Boxes
Ian Heinig

By Ian Heinig


June 3, 2021

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 to 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 70% 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.

What is USPS Priority Mail Flat Rate?

USPS Priority Mail Flat Rate is a shipping service that charges a single flat fee for all shipments weighing less than 70 pounds.

Unlike typical shipping services that are priced by weight and delivery distance, Flat Rate charges a single flat fee. USPS Priority Flat Rate shipments arrive in 1-3 days.

Packages sent via Flat Rate must use designated Flat Rate boxes or envelopes. This is because the box itself serves as the postage. Small USPS Flat Rate boxes are available on the USPS website for free.

Here’s a handful of reasons to use Priority Mail Flat Rate instead of other USPS shipping services:

  • Economical for heavy items: The cheapest way to send heavy items greater distances is often via Flat Rate. This is because Flat Rate isn’t priced by weight, dimensions, or delivery distance.
  • Easy shipping: No need to weigh or measure packages with Flat Rate. Any item that fits inside a small USPS Flat Rate box and weighs less than 70 pounds is good to go.
  • Quick delivery: Small USPS Flat Rate boxes arrive in 1-3 days, though the delivery date isn’t guaranteed.
  • Free shipping boxes: You can order USPS small flat rate boxes and flat rate envelopes free of charge from the USPS website or the local post office.
  • No surcharges: Flat Rate shipping never pays for surcharges on fuel or rural delivery.

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 Flat Rate we’re talking about – but because it looks better on the receiving end.

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

Flat Rate Envelope

  • Dimensions: 12 1⁄2 x 9 1⁄2″
  • Sized for: Small documents, passports
  • Price: $7.95

Legal Flat Rate Envelope

  • Dimensions: 9 1⁄2 x 15″
  • Sized for: Legal documents
  • Price: $8.25

Padded Flat Rate Envelope

  • Dimensions: 12 1⁄2 x 9 1⁄2″
  • Sized for: Clothing, books
  • Price: $8.55

USPS Small Flat Rate Box

  • Dimensions:  8 ⅝ x 5 ⅜ x 1 ⅝"
  • Sized For: Jewelry, small electronics
  • Price: $8.45

Medium Flat Rate Box (Top Loading)

  • Dimensions: 11 1⁄4 x 8 3⁄4 x 6″
  • Sized for: Office supplies, shoes
  • Price: $15.50

Medium Flat Rate Box (Side Loading)

  • Dimensions:  14 x 12 x 3 1/2″
  • Sized For: Shoes, office supplies
  • Price: $15.50

Large Flat Rate Box

  • Dimensions: 12 1⁄4 x 12 1⁄4 x 6″
  • Sized for: Laptops, gifts
  • Price: $21.90

APO/FPO Large Box

  • Dimensions: 12 1⁄4 x 12 1⁄4 x 6″
  • Sized for: Shipping to US military locations
  • Price: $20.40

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 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 $8.80

UPS Simple Rate Small Box

  • Maximum Size: 101-250 cubic inches
  • Sized for: A hardcover book or tissue box
  • Price: From $11.50

Read our full guide to USP 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 $9.95

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 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 – and that includes Flat Rate shipping. You save up to 70% off instantly. There’s nothing to lose.

You can create your Free Easyship account here.