UPDATE: The principles and formulas for dimensional weight (DIM weight) rules below are a great resource for ecommerce retailers. For updated examples of DIM weight formulas, including the latest DIM weight calculations and how we help you cut your shipping costs in half, visit our Dimensional Weight Calculator.


FedEx and UPS changed their dimensional weight rules starting 2015. UPS dimensional weight rules from 2015 remain in place. Fedex recently announced new dimensional weight rules for 2017. For an up-to-date overview of how DIM rules apply, please visit our most recent post: New FedEx & UPS Dimensional Weight Rules.

Have you seen those USPS commercials for their Flat Rate Boxes; you know, the ones where people are so amazed at how easy shipping is?

Well, if you’re an online merchant, you know that your stuff doesn’t always fit neatly into a flat rate box, which means that shipping isn’t always easy. Sometimes, it’s flat out complicated, especially when dimensional weight comes into play.

As an eCommerce fulfillment center, we’re often asked how to calculate dimensional weight. We’ll get into that shortly, but let’s start with a quick overview of what it actually is.

What is Dimensional Weight?

Dimensional weight, also known as “dim” weight, is a tactic used by shipping and freight companies to basically ensure they don’t lose money on lightweight packages. Dim weight has long been used for air freight, and about 5 years ago, the big shipping carriers like FedEx and UPS also started applying dimensional weight to packages shipped via ground service.

Dimensional weight works by calculating the cubic size of a package by multiplying its length, width and height. Once the dimensional weight is calculated, it is then compared to the actual weight of the package in some circumstances, and the larger of the two is used to determine the package’s actual billable weight.

When it comes to eCommerce order fulfillment, online merchants are often concerned about when dim weight will actually be triggered, and how they can anticipate those charges. So let’s talk about how to calculate dimensional weight, and when it’s applied.

How Do You Calculate Dimensional Weight?

Step 1: Measure the Package

First, grab your measuring tape and size up the length, width, and height of your package. Ensure you’re measuring from the longest points on each side. If your package isn’t perfectly square or rectangular, remember to account for any protrusions or irregularities.

Step 2: Calculate Cubic Size

Next, multiply the measurements you’ve taken to find the package’s cubic size. Let’s say, for instance, your package measures 30” long, 12” wide, and 12” high. Multiply these dimensions together and you’ll find the cubic size is 4,320 cubic inches.

Step 3: Round Off the Measurements

While calculating the dimensional weight, it’s crucial to remember that most carriers want you to round your measurements to the nearest whole number. If a measurement is halfway or more (say, 12.50 inches), round it up to the next whole number, in this case, 13”. If it’s less than halfway (12.49” or below), round down to the nearest whole number, which is 12” in this case.

Step 4: Determine Dimensional Weight

Now, the last step is to calculate the dimensional weight. Major carriers like UPS and FedEx use similar methods. For domestic shipments, they divide the cubic size of the package by 166, and for international ones, they use 139 as the divisor. However, it’s worth mentioning that in 2020, FedEx used 139 as their factor for calculating dimensional weight, whereas UPS used different factors based on rate types. They used 139 for Daily Rates and 166 for Retail Rates.

What is Dimensional Weight Pricing?

Dimensional weight pricing is defined as the price that is paid for shipping based on the cubic size of the package that is being shipped.

In many cases, the package size and overall dimensional weight are used as factors in determining the package’s billable weight, which is the final weight used to determine the actual pricing of shipping the package. But, depending on your carrier, dim weight isn’t always used to determine billable weight, and this is where it can get somewhat complicated.

box with bow

Here’s how it works. If your package is being delivered via air service, the billable weight will always be subject to dimensional weight. If it’s being shipped via ground service, however, generally it is only subject to dim weight if the cubic size of the package is 3 cubic feet or larger (5,184 cubic inches). If the cubic size is less than 3 cubic feet, dimensional weight will not apply, and the actual weight of the package will always be used.

I know, a little confusing, right? To help clear all this up, let’s take a look at a few examples below.

Example 1

Ship Method / Destination: Ground / Domestic
Actual Weight: 21 pounds
Length: 30 inches
Width: 12 inches
Height: 12 inches
Cubic Size Calculation: 30 x 12 x 12 = 4,320 cubic inches
Dimensional Weight Calculation: 4,320/166 = 26 pounds

In this first example, because it is a domestic shipment, we divide the total cubic size in inches by 166. In doing so, we find out that the dimensional weight is 26 pounds, which is greater than the actual weight.

However, because the package is being shipped via ground service and is less than 5,184 cubic inches, the dimensional weight is not applied. So in this case, the actual weight of 21 lbs. becomes the billable weight.

Example 2

Ship Method / Destination: Ground / Domestic
Actual Weight: 32 pounds
Length: 30 inches
Width: 15 inches
Height: 15 inches
Cubic Size Calculation: 30 x 15 x 15 = 6,750 cubic inches
Dimensional Weight Calculation: 6,750/166 = 41 pounds

In example 2, this is also a domestic shipment, so the cubic size in inches is divided by 166 to determine the dimensional weight, which is 41 lbs.

As in example 1, the dimensional weight here exceeds the actual weight, but because the cubic size of the package is larger than 5,184 cubic inches, the dimensional weight of 41 pounds will be used as the billable weight.

Example 3

Ship Method / Destination: Air / International
Actual Weight: 18 pounds
Length: 24 inches
Width: 12 inches
Height: 12 inches
Cubic Size Calculation: 24 x 12 x 12 = 3,456 cubic inches
Dimensional Weight Calculation: 3,456/139 = 25 pounds

In this last example, the package is being shipped internationally, so the cubic size is divided by 139 instead of 166, which makes the dimensional weight 25 lbs. This exceeds the actual weight of 18 lbs., and because it’s an air shipment and the 3 cubic foot minimum doesn’t apply, in this case the dim weight will again be used as the billable weight.



Dimensional weight can get a little confusing, and what makes it even worse is that, just when you think you have it figured it out, the carriers go ahead and change the rules (which means I’ll probably have to update this blog post before too long). And the problem with not correctly factoring in dimensional weight, is that you will likely get hit with back charges from the shipping providers.

While those USPS commercials make parcel shipping seem easy, in many cases it’s just not that simple, and that’s where an order fulfillment partner like eFulfillment Service can save you a lot of time and money.

Sick of dealing with the headaches of shipping? Let’s talk, we’d love to help.

FAQs: Dimensional Weight (DIM Weight)

What is DIM weight vs actual weight?

Dimensional weight (also known as DIM weight) is a pricing technique used by shipping companies that considers the package's volume in relation to its weight. It's a theoretical weight that can be higher than the actual physical weight of the package if the package is large but light. In contrast, the actual weight of a package is just what it sounds like—the physical weight of the package when it's put on a scale.

How do you calculate DIM weight?

To calculate DIM weight, measure the length, width, and height of your package in inches. Multiply these three dimensions to get the cubic size of the package. Then, divide the cubic size by a specific factor, which can vary based on the shipping carrier and the type of shipment (domestic or international). Commonly used factors are 166 for domestic shipments and 139 for international shipments.

What does DIM weight price mean?

DIM weight price refers to the cost of shipping a package based on its dimensional weight rather than its actual weight. If a package is large but light, the DIM weight price may be higher than if the shipping cost was calculated based on actual weight. This pricing method encourages efficient packing and utilization of space in shipping vehicles.

How does FedEx calculate DIM weight?

FedEx calculates DIM weight by multiplying the length, width, and height of a package (in inches) to get the cubic size and then dividing that number by a divisor of 139 for U.S., Puerto Rico, and international shipments. The resulting figure is then rounded up to the next whole pound.

Does USPS use dimensional weight?

Yes, USPS uses dimensional weight pricing for some types of packages. USPS applies dimensional weight pricing to packages that are larger than one cubic foot and are being shipped via Priority Mail or Priority Mail Express to zones 5-9.

How does DHL calculate DIM weight?

The process of calculating the dimensional weight with DHL involves determining the cubic size of each package by multiplying its length, width, and height. Once you have the cubic size, divide it by 166 if the measurements are in inches, or by 6000 if they're in centimeters. The resulting figure is the dimensional weight of your package. For final shipping costs, this number is compared with the actual weight of your package.

Why is dimensional weight important?

Dimensional weight is important because it ensures that the price of shipping reflects not only the weight of the package but also the amount of space it occupies. This encourages shippers to pack more efficiently and helps carriers maximize the space in their shipping vehicles. It's an important concept for anyone regularly shipping packages to understand, as it can significantly impact shipping costs.