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Understanding dimensional weight: What it is and how to calculate it

Yellow measuring tape wrapped around a shipping box with the text 'what is dimensional weight?’

For ecommerce merchants, shipping costs consistently rank as one of the biggest operational expenses. For this reason, it’s crucial to understand how dimensional weight impacts your bottom line – especially if your current packaging and shipping methods aren’t catering to this now widespread pricing technique.

In this post, we’re going to cover the basics of dimensional weight, how to calculate it, and why bringing a fulfillment provider on board will help your business to avoid any nasty surprises in shipping fees.

What is dimensional weight?

Dimensional weight, or DIM weight, is a pricing method used by commercial freight companies as well as courier and postal services. It considers the physical size of a parcel, in addition to its actual weight.

Comparing a parcel’s actual weight with its DIM weight helps shipping providers to decide how a parcel should be charged. This ensures that they won’t end up losing money when shipping packages that are lightweight but bulky – a situation that is increasingly commonplace in eCommerce.

Why is dimensional weight used?

Air freight companies have long used DIM weight to calculate shipping fees, due to space being at a premium on aircraft. However, it’s a relatively new pricing technique for courier and postal services – one that has been bought about by the rapid expansion of ecommerce over the past decade.

Since 2010, ecommerce has seen a remarkable 313% growth in revenue. This has been further exacerbated by the pandemic, with restrictions on in-store retail forcing unprecedented numbers of consumers to shop online. As parcel volumes surge along with the demand for faster shipping, shipping providers and freight companies are under increased pressure to maximize every inch of space within delivery trucks.

To make sure that they aren’t losing out from this shift towards smaller, more frequent orders, many established freight and postal services have switched over to using DIM weight. UPS, FedEx, and USPS first began using DIM weight in 2015, with USPS updating its DIM formula last year to reflect growing pressure on its network. 

Moreover, DIM weight encourages businesses to make their parcels as compact as possible so that providers can make the most of every delivery.

How to calculate dimensional weight

As mentioned above, DIM weight calculates the physical size of the package to determine whether this or the actual weight is used to determine shipping rates.

You can calculate the DIM weight of a package by doing the following: 

Multiply the width, height, and length of your package to calculate its cubic size. 

(When doing this, it’s important to consider any irregularities in the shape of the package, such as bulges or misshapen sides, as these could result in extra fees.)

Once you have the cubic size of your parcel, you need to divide this by what is known as the ‘DIM factor’. This number represents cubic inches per pound, and differs between carriers (we will cover this in the next section). The resulting factor is the DIM weight of your package.

For example, if you’re shipping a package which measures 20 x 12 x 12 inches in size, your calculation would look like this:

20 x 22 x 12 = 2880 cubic inches

Let’s say that you’re using FedEx to ship your package, who use a DIM factor of 139 for ground and domestic shipping:

2880 cubic inches / 139 = 20.7

This is rounded up to the nearest pound, meaning 21 pounds is the DIM weight of your package.

If the actual weight of your package is less than 21 pounds, the DIM weight becomes the billable weight because it’s the greater of the two. If your package weighs more than 21 pounds, it’s the actual weight that will be used.

For heavier and more compact items, such as a set of dumbbells, the DIM weight is unlikely to come into play because the actual weight will always be greater. But in the case of large, lightweight items, the DIM weight is going to determine the price of shipping.

Dimensional weight pricing for major carriers

Cubic size: Measure at the longest point, round to the nearest pound

DIM factor: 139 for Daily Rates, 166 for Retail Rates

The weight used: The greater of the two will be the billable weight.

Cubic size: Measure at the longest point, round to the nearest pound

DIM factor: 139

The weight used: The greater of the two will be the billable weight.

Note: DIM weight is not applied to FedEx packaging

Cubic size: Measure at the longest point, round to the nearest pound

DIM factor: 166

The weight used: The greater of the two will be the billable weight.

How a fulfillment partner can help

Even when you have a good grasp on how dimensional weight pricing works, calculating this within the context of ever-shifting parcel volumes and SKUs is incredibly time-consuming for merchants. 

By bringing in a fulfillment partner, you are putting your business in a much more favorable position to manage dimensional weight effectively.

They can negotiate more affordable rates

Because they manage such large parcel volumes, 3PLs are in a much stronger position to negotiate for better DIM factors than individual businesses are. This helps to keep your overall shipping costs down – especially as your operation grows.

They know how to keep billable weight down

Fulfillment providers are highly experienced in keeping the actual weight and size of packages as low as possible. Through methods such as streamlined packaging, 3PLs are well-placed to tailor a fulfillment strategy specifically to the needs of your business and merchandise.

Keeping track of changes

DIM weight calculations are always subject to change by the major carriers, and it’s all too easy for merchants to get caught out. Fulfillment providers are always up-to-date that the latest industry news, and can adapt their strategies quickly to prevent your business from incurring unnecessary costs.

Whiplash is a nationwide omnichannel fulfillment provider with over two decades of proven experience in helping businesses stay on top of industry changes.

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