What Is the Largest Box the Post Office Will Accept?

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If you need to mail a large package and want to use USPS, know that this mailing option has smaller box size and weight limits than alternatives like UPS and FedEx. USPS has some broad package-size limits for the weight and combined girth and length of packages, but these limits can vary depending on which mailing class you use and whether your package is machinable. Sending something that falls into the USPS oversize dimensions for a large package can impact whether you pay for the actual package weight.

TL;DR (Too Long; Didn't Read)

The USPS maximum size for a box would be a package sent by Parcel Select with a combined girth and length of 130 inches and a weight of 70 pounds.

Basic USPS Package-Size Limits

While a few mailing classes have their own rules, USPS has a couple guidelines to follow when determining whether you can use the service to mail your package.

First, it sets a maximum weight of 70 pounds for packages sent domestically. However, packages sent to special addresses like military bases may have an even smaller weight limit.

Second, it restricts the largest box size to have a combined girth and length of 108 inches. The girth of your package is double the sum of the two smallest measurements (often width and height).

Machinable USPS Package-Size Limits

When you're sending a box meant to be machinable, stricter requirements apply. The USPS restricts the weight to 25 pounds for most machinable shipments and 35 pounds for machinable packages using the Parcel Select service. Such packages can be no larger than 17-inches high, 27-inches long and 17-inches wide.

USPS Mailing Class Exceptions

The base size limits apply to popular mail classes such as Priority Mail and Priority Mail Express. However, some other types of USPS parcels have their own weight and/or size requirements. These include:

  • First-Class Mail: While the same size requirements apply, your First-Class parcel must weigh no more than 13 ounces.

  • Parcel Select: The combined girth and length can be up to 130 inches for this mailing class, but you'll need to pay an oversized price for this leniency.

  • Retail Ground: There's a lower weight limit of 15 pounds when your Retail Ground package has bound printed matter in it.

  • Marketing Mail: Your package must weigh at least 6 ounces and no more than 16 ounces to qualify for this option.

Handling of Large Packages

If you plan to send a large package, be aware that you may pay more than expected. For these packages, the USPS will not go by the weight alone and will calculate a dimensional weight based on the large size. Not only can this impact packages you send using the larger guidelines of Parcel Select but even Priority Mail packages that are light in comparison to the box size can be impacted.

The USPS calculation will look to see if your package's volume is under 1,728 cubic inches. If so, you'll pay the typical weight-based price. Otherwise, you'll pay whichever rate costs more.

Calculating Your Package's Size

Once you use a scale to weigh your package and get a tape measure to find the length, height and width, you have a few options to determine if your package qualifies.

To calculate manually, first add together the two smallest of the measurement values you got and double that sum to get the girth. Now, you can simply add the girth to the length to get the final value needed. For example, a package that is 14-inches long, 12-inches wide and 10-inches high would have a girth of 44 inches and a combined girth and length of 58 inches.

To save time calculating and to see real-time postage cost information, head over to the USPS website and access the USPS postage price calculator. After answering some questions about the mailing location and destination and selecting the type of packaging used, you'll go through a wizard where you enter the weight and dimensions. USPS will show an error if your weight or dimensions exceed the limits, and you'll see a list of available mailing options with prices.