If you ship products to customers, you know how hard it can be to reduce shipping costs, especially for merchants selling bulky items like suitcases, body pillows, or furniture.
Since shipping carriers consider the size of packages as well as their weight, you might be paying for the volume of the box rather than the actual weight of the contents, leading to surprisingly steep shipping costs. For businesses trying to maintain competitive prices and healthy profit margins, understanding and mitigating the dimensional weight pricing structure is absolutely critical.
Learn how dimensional weight differs from physical weight, how to calculate it, and how you can reduce dimensional weight to lower your shipping costs.
What is dimensional weight?
Dimensional weight, also known as DIM weight or volumetric weight, is a pricing technique that shipping carriers use to determine billable weight based on size in relation to the package’s actual weight.
Shipping carriers calculate DIM weight by multiplying a package’s length, width, and height and dividing that by a dimensional factor (DIM factor) chosen by a shipping carrier.
The DIM factor is used by shipping carriers to convert a package’s volume into a chargeable weight. By using this method, carriers like UPS and FedEx can assess how much space large packages take up in delivery vehicles—even if they’re lightweight—and charge for them accordingly.
Dimensional weight vs. physical weight
Dimensional weight derives from the size of a package, while physical weight refers to the actual weight of the package (typically in pounds or ounces).
Shipping companies use DIM weight pricing for large shipments that take up a lot of space and use actual package weight pricing for small or heavy shipments.
Shipping carriers including FedEx, UPS, and the United States Postal Service (USPS) pick the pricing structure based on which one is greater. So an ecommerce merchant selling large art prints online will likely pay for dimensional weight, especially if the prints are lightweight. Meanwhile, a merchant shipping small and heavy items like dumbbells or laptops will likely incur shipping costs based on physical weight.
How to calculate DIM weight
To calculate dimensional weight, find the cubic size of your package by multiplying its length, width, and height. Divide that product by your shipping carrier’s DIM factor. Here’s the calculation as a formula:
(Package length x width x height) / DIM factor = DIM weight
Since each shipping carrier chooses their own DIM factor, dimensional weight calculations can vary between carriers. Here’s how three of the largest shipping carriers in the US handle DIM weight calculations:
FedEx
Fedex uses a DIM factor of 139 for most shipping services. The shipping carrier picks whichever number is higher between physical weight and DIM weight, rounding up to the nearest whole number. So let’s say you have a package with the dimensions 24 by 18 by 5 inches that weighs three pounds.
The dimensional weight will be:
(24 x 18 x 5) / 139 = 15.54
Since this is more than the physical weight of three pounds, FedEx will charge for the dimensional weight. You can use FedEx’s dimensional weight calculator to estimate prices for specific shipments.
UPS
UPS applies a DIM factor of 166 for retail rates and packages that weigh less than one cubic foot. Retail rates apply to individual, non-contract customers.
For UPS retail rates the calculation will be:
(24 x 18 x 5) / 166 = 13.012
For packages over one foot from business accounts, UPS applies a DIM weight of 139 (known as daily rates), which means the same package would have a weight of 15.4 with the daily rate.
While it seems that the daily rate for businesses leads to a higher shipping cost than for individual customers, businesses often have access to discounts through their ecommerce platform or logistics partner. For example, you can opt into a program that offers exclusive discounted shipping rates like Shopify Shipping—Shopify’s built-in shipping software.
USPS
The United States Postal Service (USPS) uses a DIM factor of 166 to calculate dimensional weight, though DIM weight applies only to packages that exceed one cubic foot in size. This means a package of 24 by 18 by 5 inches, will have a dimensional weight of 13.02.
The USPS dimensional weight model applies to Priority Mail, Priority Express, Parcel Select, and USPS Ground Advantage. DIM weight does not impact packages shipped in USPS-provided flat-rate boxes or envelopes.
You can use the USPS Retail Postage Price Calculator to estimate the potential costs of your shipments.
Ways to reduce dimensional weight
- Use the correct size box
- Opt for lightweight packing material
- Maximize the use of space
- Work with a 3PL or shipping program
Following these shipping best practices can help you reduce the dimensional weight of your package:
Use the correct size box
Determine how much room your products require and choose boxes in which your products will sit comfortably but snugly. Minimizing empty space reduces DIM weight and costs.
Keep boxes in a variety of sizes to go with your product offerings and bundles. For example, if you sell dinnerware products online, you could keep different sizes of boxes based on your top sellers, like large plates, bowls, or cutting boards, and if your bestselling bundle is six soup bowls and six soup spoons, have a box size (or combination of boxes) that can accommodate both without too much empty space.
Opt for lightweight packing material
Research thin, lightweight packing material to protect products within packages. Thicker packing material like corrugated cardboard, packing peanuts, or plastic sheets can take up unnecessary space. By contrast, thinner material like thin foam sheets or a small amount of bubble wrap can protect non-fragile items without expanding DIM weight.
Maximize the use of space
If you’re handling your own order fulfillment process, try different product packaging arrangements to reduce the size of your packages. For example, you can disassemble products like furniture to make them fit into smaller boxes, or package each piece separately.
If you’re shipping non-fragile items like books or clothes, consider using an alternative lightweight packing option like poly mailers to minimize the empty space.
Work with a 3PL or shipping program
Third-party logistics (3PL) companies can help bring down the shipping cost of packages using DIM weight since they have their own shipping infrastructure and materials. 3PL companies negotiate lower rates with major carriers through high-volume contracts. They can also optimize packaging with the right-sized boxes and advanced software, minimizing wasted space. Some 3PLs also use their own regional networks, bypassing standard carriers for certain deliveries. These actions collectively lower shipping costs for their clients.
Similarly, programs like Shopify Shipping can help you get pre-negotiated discounted rates. It allows Shopify merchants to manage order fulfillment from one dashboard and get access to pre-negotiated discounted shipping rates from major carriers like FedEx and UPS.
Dimensional weight FAQ
Does USPS use dimensional weight?
Yes, the United States Postal Service (USPS) uses dimensional weight as well as actual weight to find the billable weight for the packages they deliver, typically choosing whichever is greater. However, the USPS dimensional weight pricing model applies only to packages that exceed one cubic foot in size.
What is the difference between dimensional weight and actual weight?
Dimensional weight relates to the size of your shipment, whereas actual weight comes from the physical weight of a package (in pounds or ounces, for instance).
How do you avoid dimensional weight charges?
To lower dimensional weight charges, choose appropriately sized boxes, arrange items well, opt for thin packing material, and work with a good 3PL or shipping program to optimize your order fulfillment process.
What is an example of dimensional weight?
An example of dimensional weight would be a merchant shipping lightweight bedding material in a large box with a length of 24 inches, a height of 12 inches, and a width of 16 inches. Using FedEx for this shipment, the merchant could calculate their dimensional weight like this: (24 x 12 x 16 = 4608 cubic inches) / 139 DIM factor = 33.15 (rounded up to a DIM weight of 34).
