Maximum Box Dimensions for Shipping With USPS

Before you start shipping or start to create custom packaging for your business, it’s good to be aware of the maximum box dimensions to ship with the US Postal Service. We’ve listed all of that information below for the corresponding mail classes. First, you’ll need to know what the girth of your package is.

Table of Contents

• How to Calculate the Girth of Your Package
• Maximum Dimensions for Domestic Mail Classes
• Maximum Dimensions for International Mail Classes
• What About Minimum Dimensions?
• Beware of New Non-Standard Fees from USPS

How to Calculate the Girth of Your Package

To calculate your package’s girth, take the two smaller dimensions of your package (we’ll use Width and Height in this example), and add those two numbers together. Then, multiply that sum by 2 to get the Girth. The formula should look like this:

Girth = 2*(Width + Height)

Maximum Dimensions for Domestic Mail Classes

First-Class Package

• Maximum Dimensions: 22″ x 18″ x 15″

Priority Mail

• Maximum Length + Girth: 108 inches

Priority Mail Express

• Maximum Length + Girth: 108 inches

Priority Mail Cubic

• Maximum Dimensions for boxes: No one dimension can exceed 18 inches, and total volume can’t exceed 0.5 cubic feet
• Maximum Length + Width for poly mailers and envelopes: 36 inches

Retail Ground (or Parcel Select Ground)

• Maximum Length + Girth: 130 inches

Maximum Dimensions for International Mail Classes

First-Class Package International

• Maximum Dimensions: 24″ in Length, Length + Width + Height: 36″

Priority Mail International

• Maximum Length + Girth: 108 inches (varies by country—check USPS’ individual country codes for restrictions)

Priority Mail Express International

• Maximum Length + Girth: 79 inches (varies by country—check USPS’ individual country codes for restrictions)

What About Minimum Dimensions?

They say good things come in small packages…but USPS does have a minimum package size requirement! When shipping a box, the minimum dimensions are 6x3x0.25″. This rule applies for any USPS mail class you decide to ship in.

USPS could technically reject your package if your box is smaller than those dimensions, but the chances of that happening are pretty rare. However, we always suggest using a box that’s at least as big as the minimum dimensions. If there’s no way for you to do that, we recommend putting the box into a small poly mailer envelope when you ship it.

Pro Tip: If you use free USPS boxes, you won’t have to worry about minimum dimensions at all…but you may have to worry about some new surcharges if you exceed certain dimensions! We’ll get into that below, but in the meantime, you can check out our guide that lists the dimensions of all the free USPS boxes if you’re in the market for some free packaging.

Beware of New Non-Standard Fees from USPS

In April 2022, USPS began imposing “non-standard fees” on packages, which are basically surcharges for being over a certain size. USPS never hit shippers with surcharges the same way UPS and FedEx did, but the Postal Service introduced these new surcharges in order to offset inflationary pressures from rising fuel and transportation costs.

The new USPS non-standard fees are as follows:

• $4 if any length of your package exceeds 22 inches but is less than 30 inches
• $15 if any length of your package exceeds 30 inches
• $15 for packages greater than 2 cubic feet in volume
• $1.50 for missing or incorrect dimensions that result in any of the above non-standard surcharges; you can think of this as an “overdraft” fee that USPS charges for imposing any of these non-standard fees

To learn more about these new USPS surcharges, check out our article: USPS Non-Standard Fees: A Guide to Understanding the New USPS Surcharges.