Dim Weight Calculation: How to Calculate 

As of 2015, shipping carriers are no longer just using a package’s actual weight and the distance it has to travel to calculate shipping costs. Today, the actual weight and the volume the package takes up are both considered. 

The dimensional weight, or DIM weight, of a package relates to how much space the package takes up. If this is greater than the actual weight of the package, DIM weight is used for shipping costs. If the package’s actual weight is more than the DIM weight, that is used to calculate shipping costs.

Due to DIM weight being a factor in shipping costs, it is even more important to ensure that your packages are as small as they can be while also protecting the items you are shipping and allowing for packing materials. A large box, even if it is lightweight, can cost more than a smaller, heavier one. 

Every carrier has a slightly different formula and method for calculating DIM weight.

What Is Dimensional Weight?

Dim weight, or dimensional weight, takes into consideration the size of the package you are shipping in relation to its actual weight. Package volume is used in addition to weight when calculating dim weight. In general, dim weight is calculated by taking the package length and multiplying this by the height and the width to find the package volume. 

DIM weight helps to lower the amount of space a package can take up. Since there is limited space on delivery trucks, it is more cost-effective and ecologically friendly to use smaller boxes when possible. You will be charged based on whichever is greater, the dimensional weight or the actual weight of your package.

How to Calculate DIM

To calculate dimensional weight, measure the length, width, and height of a package and divide it by the carrier’s divisor. You will use the cubic size of the package in inches divided by the DIM divisor to reach the package’s dimensional weight in pounds. If your package is not perfectly square, you will measure the package at its longest points and round up. 

Use these steps to calculate DIM weight:

1. Using the longest points on each side, measure the length, width, and height of your package. If your package is irregularly shaped on any side or has bulges, be sure to take these into account and measure at the longest point to avoid special handling fees.
   
2. Typically, you will need to round your measurements up to the next whole number.
   
3. Multiply these package dimensions to come up with the cubic size of your package in inches. For example, if your package is 25 inches by 10 inches by 10 inches, the cubic weight would be 2,500 cubic inches, which is the product of these three measurements multiplied together.
   
4. Each major shipping carrier has a dimensional factor, or a DIM divisor, that represents cubic inches per pound. USPS uses a DIM divisor of 166, for instance, while FedEx uses 139 as their DIM divisor. 

In the previous example, the DIM weight would be 15.06 pounds for USPS, while with FedEx, the DIM weight would equal 17.99, or 18 pounds. If the package weighs more than 15 or 18 pounds (based on the carrier), the pricing will be based on this instead of the DIM weight. If the DIM weight is greater, that calculation is used for billing.

DIM Calculators by Carrier

Every major carrier calculates DIM weight slightly differently, and each provides a calculator to help you estimate DIM weight before shipping. Carriers can use different divisors based on how far the package must travel along with other factors.

USPS

When shipping packages with the USPS (United States Postal Service), if the package exceeds 1,728 cubic inches, its volume will need to be divided by the DIM divisor of 166 to find its weight in cubic pounds. To find the DIM weight for USPS, use the following formula:

Length x width x height / 166 = cubic weight in pounds

Each of these measurements is to be rounded up to the next whole number. If your package is not rectangular, you will need to multiply the result of the length times width times height with an adjustment factor of 0.785. If the dimensional weight exceeds 70 pounds, you will pay the 70-pound price.

UPS

To calculate the cubic size of your package in centimeters for UPS, you will use the following formula:

Length x width x height (each rounded up to the nearest centimeter) = total cubic size

To calculate dimensional weight, you will divide the total cubic size in centimeters by 5,000 and increase this number to the nearest kilogram. You will then need to determine if the actual weight or the DIM weight is greater for your billable weight.

FedEx

FedEx provides a dimensional weight calculator that you can use to find the DIM weight of your package. Simply type the length, width, and height (in inches and each rounded to the next whole number) into the provided calculator and click “calculate.” The DIM weight will be found using the following formula:

Length x width x height / 139 = cubic weight in pounds

Just as with the other carriers, the billable weight will be whichever is larger, the DIM weight or the actual weight of your package. DIM weight applies to both FedEx Ground and FedEx Express. 

Flat-rate shipping for each carrier does not take DIM weight into account as long as the package does not exceed the weight requirements and fits into the appropriate packaging.

References

What Is Dimensional Weight? (2022) FedEx.

Postal Explorer. (2022). USPS. 

Dimensional Weight. (2022). United Parcel Service of America, Inc.

Dimensional Weight Calculator. (2018). FedEx.