Dimensional (DIM) Weight

As a shipper, you may have heard of the term Dimensional weight (DIM weight) before, but do you know exactly what it means? DIM weight is the theoretical weight of a package based on the length, height, and width of the box. This concept of theoretical weight is practiced across the board in the transportation industry worldwide as the uniform means of establishing a minimum charge for cubic space a package occupies. If the actual weight of the package is less than the dimensional weight, the dimensional weight will be used to determine the cost of shipping. The DIM weight surcharge is by far the most significant of additional surcharges. Shippers are charged dimensional because large boxes that weigh little take up too much volume (space in the aircraft) for the revenue they produce on a per-pound basis.

FedEx shipping rates are based on the assumption that, on average, each cubic foot a box occupies weighs about nine pounds. If a box is lighter than this, there is a formula used to calculate the dimensional weight charge.

Below is an illustration of the formula used to calculate a dimensional weight fee. A box that is 35” x 14” x 12” but only weighs ten pounds is considered too light. To calculate the formula, multiply the dimensions in inches (35 x 14 x 12, which equals 5,880) and divide that number by 166. The result is 35.42168. That number is always rounded up, in this case to 36.  That means that this ten-pound box will be charged as if it weighs 36 pounds.

The best way to track and control dimensional weight cost is to set a minimum weight for each type of box you use.  For example, in the chart below we have listed the three most common sizes of boxes our clients use, the typical weight range for each box, and the minimum weight required to avoid a dimensional weight surcharge.  If you provide a list of all of the boxes used for your shipments, we will set up a chart like the one below that can be used as an order guide by your sales and operation personnel.

Typical weight
Typical weight Range
Minimum Weight to Avoid “Dim” charges
28” x 13” x 8”
20 – 30 pounds
18 pounds
34” x 14” x 12”
30 – 60 pounds
35 pounds
37” x 19” x 14”
60 – 100 pounds
59 pounds


How to Avoid DIM Weight Surcharge

  • Combine orders when possible.
  • If there happens to be an abundance of void space within a box, consider decreasing the size of the box.
  • Take advantage of the PeriShip DIM weight calculator on the Customer Portal. It can easily calculate the DIM weight of any package you are sending.

If you have any further questions on DIM weight and if it will impact your shipments, we encourage you to contact PeriShip at info@periship.com. We will individually analyze your packaging and shipping practices to help avoid the DIM weight surcharge.

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