The United States Postal Service (USPS) faces stiff competition from a number of national and regional parcel delivery services, but it remains a cost-effective way to put your product into customers' hands. Sending either bulky merchandise or merchandise in bulk often requires a large box, so it's useful to know how the USPS measures those and what its size limits are.

Length and Girth

USPS package size limits are based on the package's length, width and height, but the limits aren't always expressed in exactly that way. The service uses a measure called "girth" as part of its size calculation, which can be a bit of a curveball if you aren't expecting it.

It's essentially the same measurement you make when you put a measuring tape around your own waist. To calculate the girth of your package, and determine whether it fits USPS large package guidelines, measure its width and depth. These are the two shorter sides, not the longest side. Now, multiply each of those measurements by two and add them together. For example, if your box had a height of 11 inches and a width of 14 inches, the math would look like this: 2 X 11 inches = 22 inches, 2 X 14 inches = 28 inches, and 22+28 inches equals a total girth of 50 inches.

The USPS sets a ceiling for most parcels based on the package's length plus its girth, which limits the package's size in cubic inches. That tells the USPS how many packages it can physically fit into one vehicle, so it's an important measurement.

USPS Package Size Limits

Commercial parcels can be quite a bit larger than the USPS "large box," familiar from the service's popular flat-rate retail shipping program. For regular commercial shipping through USPS, the size limits for your packages are as follows:

  • Weight: 15 pounds for "Bound Printed Matter," such as catalogs or sales materials, and 70 pounds for all other content. 
  • Length plus girth: No more than 108 inches in total.

If you meet the volume requirements to ship through Parcel Select, rather than regular USPS Retail Ground service, you have leeway to send slightly larger parcels:

  • Weight: Again, no more than 70 pounds maximum.
  • Length plus girth: Up to 130 inches in total.

If you have a relatively restricted range of products you'll be shipping through USPS, you may find it's a convenience and time-saver to purchase boxes in a handful of standardized sizes. That way, you'll always know the length and girth and won't need to do the math for every single parcel. If you're going to be shipping a wide variety of parcels in different sizes, or if your shipping volume doesn't justify purchasing boxes in bulk, you can simplify the math and avoid human error by using the USPS girth calculator on the service's website.

Scaling Down to Machinable Package Sizes

In some cases, it may be more cost-effective for you to use a package size that's less than the maximum. The USPS classes some parcels as "machinable," meaning they meet the size limits of the automatic sorting machines at USPS distribution centers. Machinable parcels are cheaper for the USPS to process, so they're lower cost for you as well. The limits for machinable parcels are:

  • Weight: 25 pounds, or up to 35 pounds if you're using Parcel Select.
  • Physical dimensions: Not more than 27 inches in length, and not more than 17 inches wide or deep.

International Package Size Limits

For packages with an international destination, the USPS uses the same limits of 70 pounds maximum weight and a total of 108 inches for length and girth. However, you'll also need to be aware of size and weight restrictions imposed by the receiving country's postal service. The USPS maintains a chart of weight limits by country, for your convenience.

Packages going to most countries by Global Express can weigh up to 70 pounds like domestic parcels, but those shipped Priority Mail Express International face more variable limits. Canada's postal service accepts packages of up to 66 pounds, for example, while Bermuda's limit is 44 pounds and the Bahamas' is just 22 pounds.