Shipping & Fulfillment

Shipping: Dimensional Weight Errors Can Cost Big Bucks

There are mistakes that can cost you when calculating shipping and handling fees. A big one is missing a UPS, FedEx or U.S. Postal Service DIM (dimensional) or oversize rule for large or lightweight packages.

The term “DIM” refers to package shipping density, meaning the weight of the package in pounds per cubic foot. If your package is big enough, or if the weight is small enough, the DIM rules can make your shipping costs dramatically increase.

For example, to ship a carton as small as 18” x 18” x 18”, UPS and FedEx DIM rules substitute 31 pounds as the minimum billing weight, even if the actual weight is much less. Or, for a carton as small as 27” x 27” x 27”, UPS and FedEx will add a $45 oversize surcharge on top of the DIM weight.

How UPS and FedEx DIM Rules Work

If the shipping carton exterior dimension (length x width x height) volume is greater than 5,184 cubic inches (3 cubic feet), divide the carton volume by 194. The resulting number is the arbitrary DIM weight, which becomes the billable weight if it exceeds the actual weight.

For example, assume there’s a box with a volume of 36″ x 24″ x 12″, which is 10,368 cubic inches. Divide this volume, 10,368 cubic inches, by 194 equals a DIM weight of 54 pounds. If the actual ship weight is 10 pounds, the UPS or FedEx residential ground zone 5 delivery cost would be $13.50; but, taking into account the 54 pound DIM weight, the fee increases to $36.36 – a cost increase of $22.86, or 170 percent.

DIM Rules Are Different for Air Shipments

For UPS and FedEx air-express shipments, the same DIM calculation process applies, but without the 3-cubic-foot minimum. That means a typical carton size like 12″ x 9″ x 6″ has a DIM weight of 648 cubic inches divided by 194, or 3.34 pounds, which rounds up to a 4 pound billable weight, even if the actual weight is much less.

Additional Fee For Oversize Cartons

There is a special UPS and FedEx rule for oversize packages, which is defined as length (the longest side) plus the girth (width x 2 plus height x 2) totaling more than 130 inches, but less than a 165 inch maximum size limit. A $45.00 surcharge is added to the DIM or actual weight delivery cost for such oversize packages.

U.S. Postal Service Priority Mail Rules Are More Complicated

For U.S. Postal Service Priority Mail zones 1 through 4, the minimum DIM weight is 20 pounds if the length plus the girth add up to more than 84 inches, but less than the 108 inch maximum size.

There is a different rule for Priority Mail zones 5 through 8. If the package volume exceeds one cubic foot (1,728 cubic inches), divide the cubic inches (L x W x H) by 194 to get the DIM weight. But, importantly, note that all U.S. Postal Service provided Priority Mail and Flat Rate cartons are excluded from the DIM rules.

For example, for a Priority Mail package that weighs 9 pounds with a length of 60 inches, width of 8 inches and height of 6 inches, the DIM weight for zone 1 through 4 is 60″ + (2 x 8″) + (2 x 6″) = 88 inches, which exceeds the 84 inch benchmark, making the DIM billable weight 20 pounds, far exceeding the actual weight of 9 pounds.

For the same size Priority Mail package sent to zone 5 to 8, the DIM weight calculation would be 60″ x 8″ x 6″ = 2,880, which divided by 194 equals 15 pounds billable weight and takes the place of the 9 pound actual weight.

U.S. Postal Service Parcel Post Rules Are Even More Complicated

For U.S. Postal Service Parcel Post packages, there is a 20 pound minimum if the combined length plus girth exceed 84 inches, but is less than 108 inches. If the length plus girth exceeds 108 inches, but is less than the 130 inch size limit, you must use U.S. Postal Service oversized rates, which range from $61.80 for zones 1 and 2 to $107.16 for zone 8, regardless of the actual weight.

The DIM Factor for International Shipments

For U.S. Postal Service, UPS and FedEx international packages, including UPS and FedEx ground-Canada shipments, the DIM factor used is 166 rather than 194. For example, for an international package sized 14″ x 12″ x 9″, the DIM weight works out to 1,512 cubic inches divided by 166, which equals 9.1 pounds, and rounds up to a minimum billable weight of 10 pounds.

A Spreadsheet Makes Rate Shopping Easier To Manage

A spreadsheet that figures the DIM weights for your stock box sizes can help to determine complex shipping calculations. Click here to download a working version of the spreadsheet that I use.

To use the spreadsheet, enter the length (the longest side), the width and the height in inches for each of your stock shipping cartons, rounding fractions up or down to an even inch. The resulting DIM weights and oversize fees are displayed for each domestic carrier and delivery type.

More DIM Resources Are Available Online

If you would like to learn more about DIM calculation rules and pricing, here are some informative web pages.

Four More Cost Saving Tips

  1. Share copies of this article and your stock carton DIM spreadsheet with your staff to alert your customer service and shipping personnel of the current DIM and oversize shipping rules.
  2. When choosing shipping cartons, if possible, adjust your length x width x height dimensions to avoid creating a DIM surcharge for your typical ship weights, as a single wasted inch can make a big difference in certain circumstances.
  3. When entering dimensions into carrier systems like UPS WorldShip or U.S. Postal Service at, keep in mind that full inch DIM dimensions are rounded up and down (i.e., a length between 11.1- to 11.49-inches would round down to a DIM length of 11 inches; a length between 11.5- to 11.99-inches would round up to 12 inches).
  4. Even if you don’t run into a DIM or oversize problem, you should always pay close attention to your actual package ship weights as an extra carton or dunnage weight of as little as one tenth of an ounce can push the billable weight to the next higher per-pound rate, which after hundreds of shipped orders can add up to thousands of dollars of wasted expense.


U.S. Postal Service, UPS and FedEx DIM weight rules are complicated, but if your company ships large cartons, lightweight products, or ships via UPS or FedEx air express, it is vital that you factor in the DIM minimums and oversize rules when you calculate your final shipping and handling fees to the end customer.

John Lindberg
John Lindberg
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