Shipping costs aren’t always based on how much a package weighs. Carriers also consider how much space a shipment occupies, using a pricing method known as dimensional weight or DIM weight. Learning how to determine dimensional weight can help businesses better predict shipping costs, identify inefficient packaging, and avoid unnecessary dimensional weight charges.
Table of Contents
- What Is Dimensional Weight?
- How to Calculate Dimensional Weight
- Dimensional Weight vs. Actual Weight
- Tips to Reduce Dimensional Weight Costs
- How a Fulfillment Partner Helps
- Frequently Asked Questions
- Understanding Dimensional Weight Can Lead to Smarter Shipping
What Is Dimensional Weight?
Dimensional weight is a calculated shipping weight based on the amount of space a package occupies rather than simply how much it weighs on a scale.
Think about a large box containing a lightweight product. The package may weigh only 5 pounds, but because it occupies considerably more room in a delivery truck, trailer, aircraft, or sorting facility than a typical 5-pound package, the carrier may charge as though it weighs considerably more.
That calculated weight is the package's dimensional weight, sometimes called DIM weight or volumetric weight.
Carriers calculate dimensional weight using the package's length, width, and height along with a number called a dimensional factor or DIM divisor. The divisor converts the package's cubic volume into a theoretical shipping weight.
Major parcel carriers use dimensional weight pricing, although the divisor, measurement rules, rounding methods, and applicability can vary by carrier, service, and shipping agreement. Businesses should therefore verify the applicable DIM divisor rather than assuming that every shipment will use the same calculation.
Why Do Carriers Use Dimensional Weight?
Transportation networks have limited physical capacity. A truck can reach its maximum usable space before reaching its maximum allowable weight.
Consider two 5-pound shipments. One fits inside a compact 10" × 8" × 6" box, while another requires a 24" × 18" × 16" carton. Although both packages have the same actual weight, the second consumes substantially more transportation capacity.
Charging strictly according to actual weight would not accurately reflect that difference.
Dimensional weight pricing allows carriers to account for both weight and space utilization. This encourages shippers to use more efficient packaging while helping carriers maximize the capacity of their transportation networks.
Dimensional pricing became especially important in the U.S. parcel market following industry-wide changes that expanded the application of DIM pricing beginning in 2015. Today, understanding DIM weight is an important part of managing parcel shipping costs.
How to Calculate Dimensional Weight
The basic dimensional weight calculation is straightforward. You need three pieces of information:
- Package length
- Package width
- Package height
Once you have those measurements, calculate the cubic volume of the package and divide it by the appropriate dimensional factor.
The Dimensional Weight Formula
The basic formula is:
Dimensional Weight = Length × Width × Height ÷ DIM Divisor
For domestic measurements in inches, 139 is a commonly used dimensional divisor for many parcel shipments, but businesses should always confirm the divisor that applies to their specific carrier, service, and negotiated agreement.
For metric calculations, a divisor such as 5,000 may be used when dimensions are measured in centimeters.
Let's look at an example.
Suppose you're shipping a package measuring:
20" long × 16" wide × 12" high
First, determine its cubic volume:
20 × 16 × 12 = 3,840 cubic inches
Using a dimensional factor of 139:
3,840 ÷ 139 = 27.63
After applying the carrier's required rounding rules, the dimensional weight would typically be 28 pounds.
Now suppose the actual package weight is only 15 pounds.
Because the dimensional weight is higher than the actual weight, the shipment may be rated at 28 pounds rather than 15 pounds. That difference can have a significant impact on shipping costs, particularly when repeated across thousands of orders.
Measuring Your Package Correctly
Accurate measurements are essential for dimensional weight calculations.
Measure the outside dimensions of the finished package, not the inside dimensions of the carton. The carrier is concerned with the amount of physical space the shipment occupies in its network.
Depending on the carrier's measurement rules, fractional dimensions may need to be rounded to whole inches. A package measuring slightly over a whole-inch dimension can therefore have a higher calculated volume than expected.
Packaging materials also matter. Void fill, cushioning, inserts, protective materials, and oversized cartons can increase the exterior dimensions of the finished shipment.
For example, reducing a box by only a few inches may not seem significant. But because dimensional weight multiplies all three dimensions, small reductions in length, width, and height can combine to produce a meaningful reduction in billable weight.
Dimensional Weight vs. Actual Weight
Understanding the difference between dimensional weight and actual weight is critical when estimating parcel shipping costs.
Actual weight is simply what the finished package weighs when placed on a scale.
Dimensional weight represents the theoretical weight of the package based on the space it occupies.
For shipments subject to DIM pricing, carriers generally compare the two and use the greater value to establish the billable weight.
For example, consider this shipment:
Package dimensions: 24" × 18" × 12"
Actual package weight: 20 pounds
DIM divisor: 139
First, calculate the dimensional weight:
24 × 18 × 12 = 5,184 cubic inches
Then divide by 139:
5,184 ÷ 139 = 37.29
Subject to the applicable carrier rounding rules, the DIM weight would be approximately 38 pounds.
That gives us:
Actual weight: 20 pounds
Dimensional weight: 38 pounds
Billable weight: 38 pounds
Even though the package physically weighs only 20 pounds, its size may cause it to be rated as a 38-pound shipment.
Now imagine that same scenario across 5,000 or 10,000 packages per month. Packaging decisions can quickly become a major contributor to overall transportation spend.
This is why businesses shouldn't look only at product weight when forecasting shipping costs. Package dimensions can be equally important.
Tips to Reduce Dimensional Weight Costs
Businesses can't eliminate dimensional pricing, but they can take steps to reduce its impact.
Right-size your packaging. Avoid using a standard oversized box simply because it's convenient. Maintaining an appropriate assortment of carton sizes can help match packaging more closely to product dimensions.
Reduce unnecessary void space. Excessive air pillows, paper, foam, and other void-fill materials can require a larger carton. The goal is to protect the product adequately without creating unnecessary package volume.
Review packaging regularly. Product assortments and order profiles change over time. Packaging that made sense two years ago may no longer be appropriate. Compare carton utilization, dimensional weight calculations, and carrier invoices to identify opportunities for improvement.
Consider alternative packaging. Soft or flexible products may sometimes be shipped in poly mailers or other lower-volume packaging rather than corrugated boxes, provided the packaging offers appropriate protection and complies with carrier requirements.
Consolidate orders intelligently. When customers purchase multiple products, packing those items efficiently into one appropriately sized carton may be more economical than sending several separate shipments. However, consolidation should be evaluated carefully because a larger carton can also increase dimensional weight.
The best packaging strategy balances several factors at once: product protection, material cost, labor efficiency, customer experience, actual weight, dimensional weight, and transportation cost.
How a Fulfillment Partner Helps Reduce DIM Weight Costs
Dimensional weight becomes more difficult to manage as order volume and SKU count increase.
An eCommerce operation shipping a handful of products may be able to select packaging manually. A company shipping thousands of orders across hundreds or thousands of SKUs faces a much more complicated optimization problem.
That's where an experienced third-party logistics provider can help.
At a2b Fulfillment, packaging and shipping decisions are part of the broader fulfillment process. Rather than viewing shipping as a separate transaction, we look for opportunities to improve efficiency from the moment an order enters the fulfillment operation through final delivery.
A 3PL can help businesses evaluate carton selection, product dimensions, packaging materials, order profiles, and carrier options. Technology can also help identify products and order combinations that consistently generate high DIM weights.
Packaging optimization is only one side of the equation.
Carrier strategy matters as well. Shipping costs depend on factors including package characteristics, destination, service level, carrier pricing, surcharges, and the shipper's negotiated rates and terms. An experienced fulfillment partner can help determine the most appropriate shipping solution based on the characteristics of each order.
For growing brands, even relatively small improvements can become significant at scale. Saving a few cubic inches on one package doesn't sound transformative. Reducing dimensional weight across tens or hundreds of thousands of annual shipments is another story.
Understanding Dimensional Weight Can Lead to Smarter Shipping
Dimensional weight is more than another carrier calculation. It's an important indicator of how efficiently you're using packaging and transportation capacity.
To determine dimensional weight, multiply the package's length, width, and height and divide the result by the applicable DIM divisor. Then compare that result with the package's actual weight. For shipments subject to DIM pricing, the higher weight generally determines the billable weight.
Businesses can reduce dimensional weight costs by right-sizing packaging, minimizing unnecessary empty space, evaluating alternative packaging, and regularly reviewing shipping data.
For companies shipping at scale, a fulfillment partner can make that process significantly easier.
Ready to identify opportunities to reduce dimensional weight and shipping expenses? Contact a2b Fulfillment to discuss your packaging and fulfillment strategy and start shipping smarter.
Frequently Asked Questions
How do you determine dimensional weight for a package?
To determine dimensional weight, multiply the package's length, width, and height to calculate its cubic volume. Divide that figure by the dimensional divisor specified by your carrier or shipping service. The resulting figure is the package's dimensional weight, subject to the carrier's applicable rounding rules.
What is the formula for dimensional weight?
The basic dimensional weight formula is:
Length × Width × Height ÷ Dimensional Divisor = Dimensional Weight
Measurements are commonly taken in inches for U.S. parcel shipments. The appropriate divisor can vary depending on the carrier, service, and shipping agreement, so businesses should verify the correct dimensional factor before calculating DIM weight.
Why do carriers use dimensional weight?
Carriers use dimensional weight because package size affects transportation capacity as well as package weight. A large, lightweight package can consume substantially more space in a truck or aircraft than a compact package of the same actual weight. Dimensional weight pricing accounts for that difference.
Is dimensional weight the same as actual weight?
No. Actual weight is the physical weight of a package measured on a scale. Dimensional weight is a calculated weight based on the package's exterior dimensions. For shipments subject to dimensional pricing, the carrier generally compares the two and uses the greater value to determine the billable weight.
How can businesses reduce dimensional weight costs?
Businesses can reduce dimensional weight costs by using right-sized packaging, minimizing unnecessary void space, selecting alternative packaging when appropriate, and regularly reviewing package dimensions against carrier charges. Working with an experienced fulfillment provider such as a2b Fulfillment can also help businesses optimize packaging and shipping strategies across a larger volume of orders.
