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Dimension Weight Calculation: Understanding DIM Weight

Shipping carriers run a business. If eCommerce stores were able to hack or circumvent shipping costs and defer them to the carriers, their profit margins would plummet. Dimensional weight or DIM weight calculation is how carriers ensure that they are not overpaying for shipping your business’s products.

Dimensional weight takes into account not only a package’s weight but also the dimensions of the box. Carriers then charge your business for the highest of the two calculations, to ensure that they do not overpay on their end for large, light boxes.

This pricing technique will be part of your fulfillment process. Therefore, understanding DIM weight yourself or recruiting a third-party fulfillment company to manage it for you is a vital step in building your business’s shipping system.

In this article, we discuss:

  • What is dimension weight calculation?
  • How do carriers calculate DIM weight?
  • Why is it important in eCommerce?
  • How can a 3PL help?

What is dimension weight calculation?

Dimension weight, dimensional weight, or just DIM weight is used by commercial freight carriers, even your local postal service, to figure out how much it costs to ship packages whose physical size and weight are drastically different.

Consider that a large box takes up space in a carrier’s delivery truck, which makes it necessary for them to make more trips or have more drivers on call, costing them money. Even if the box is light, they have to front these costs.

This means that without a way to calculate shipping charges on packages independently of weight, businesses that sell large, light products would be a huge drain on the mail carrier’s profits. This includes drapes, bathroom rugs, lightweight appliances and chairs, and more.

How do carriers calculate DIM weight?

To account for limited space in delivery vehicles, DIM weight calculates shipping charges using volume. They can then compare this number to the weight calculation and charge eCommerce businesses based on whichever number is higher since that’s the number that will help them maintain their own profit margins.

The major mail carriers like UPS, USPS, and FedEx calculate weight and DIM weight during the billing process. Your business should too if you want to plan for shipping costs. However, each mail carrier uses different calculations to arrive at the billable DIM weight.

UPS and USPS use similar calculations to determine DIM weight. For example, using their online tools, a box with dimensions 16x10x6 has a dimensional weight calculation of 5.783 pounds. However, the same box shipped through FedEx has a DIM weight of 6.9 pounds. The reason they differ is in their interpretation of the DIM calculation process.

How to Calculate DIM Weight

To understand how shipping carriers’ calculations differ or to calculate DIM weight in your own business, here are the steps required to arrive at a package’s DIM weight.

  1.     First, you need to calculate the package’s dimensions. For a rectangular box, this is simple – just take the longest point on every side and measure in a straight line. For irregular boxes, you need to make sure that you include lumps or weird shapes into your assessment of the side’s length. A carrier may charge an extra handling fee if you don’t. Round the length of the sides up to a whole number.
  2.     Multiply these numbers together to get an approximation of the box’s volume. For example, using the box mentioned about, 16x10x6 = 960 cubic inches.
  3.     Lastly, divide this number by the “dimensional factor.” This is a coefficient (sometimes called the “DIM divisor”) that is established by each mail carrier to determine their individual costs for dimensional weight. This is how different mail carriers can have different DIM weight calculations.

To summarize, if you plan on shipping a box with dimensions 16x10x6, you would multiply them together (960 cubic inches) and divide by the dimensional factor. In the case of FedEx, this number is 139 cubic inches/pound. Therefore, 960/139 = 6.9 pounds of DIM weight.

If your box weighs only 3 pounds on a scale, this means that factoring in the dimensions will result in higher shipping charges. Carriers would use the DIM weight to bill you in that case. But if the package weighs 10 pounds, that will be the number they use since it’s the more costly dimension.

Why is DIM Weight Important in Ecommerce?

Shipping charges represent a major aspect of your fulfillment process, one that must be optimized if you hope to make your business as profitable as it can be. DIM weight is used by major mail carriers to ensure that they are not losing money by shipping your packages.

Therefore, it should be used by your packing team to determine how your items should be shipped to save your business money. Knowing how your products will be billed ensures that you can control costs and cut them when possible.

A 3PL like eWorld Fulfillment knows how to calculate DIM weight for the major mail services. Their relationship with carriers can also secure your business shipping discounts. These are in addition to the costs they can cut by refining your shipping process itself, from making use of free shipping supplies to properly calculating a package’s billable weight.

The Takeaway

Dimensional weight is a crucial component of calculating fulfillment costs. Since mail carriers use it to bill your business’s packages based on their dimensions, many eCommerce businesses will be charged more than they expect once they begin shipping their merchandise.

A 3PL can make your team aware of these costs and navigate them for you. Since different carriers use DIM weight differently, a 3PL’s shipping infrastructure can come in handy navigating those differences, saving your business resources during the packing process and profits after shipping calculations.