Each shipping company has their own set of rules to determine dimensional weight. Please reference the dimensional calculation from your Shipping Company.
Dimensional weight, used in shipping and freight, is a billing technique which takes into account the length, width, and height of a package.
If your package has a large size-to-weight ratio, you may need to consider your package's dimensional weight when calculating your shipping rates.
Learn About Dimensional Weight
Dimensional weight is a calculation of a theoretical weight of a package. This theoretical weight is the weight of the package at a minimum density chosen by the freight carrier. If the package is below this minimum density, then the actual weight is irrelevant as the freight carrier will charge for the volume of the package as if it were of the chosen density (what the package would weigh at the minimum density). Furthermore, the volume used to calculate the Dimensional Weight may not be absolutely representative of the true volume of the package. The freight carrier will measure the longest dimension in each of the three axis (X,Y,Z) and use these measurements to determine the package volume. If the package is a right-angled rectangular cuboid (box), then this will be equal to the true volume of the package. However, if the package is of any other shape, then the calculation of volume will be more than the true volume of the package.
Dimensional weight is also known as DIM Weight, volumetric weight, Cubed Weight, etc. Freight carriers utilize the greater of the actual weight or dimensional weight to calculate shipping charges. Dimensional Weight is calculated as (Length x Width x Height) / (Dimensional Factor). Measurements can be made all in inches or all in centimeters, but the appropriate shipping factor must also be used.
Determining which weight to use in calculating your rate requires that you determine which rule applies. Dimensional weight reflects package density, which is the amount of space a package occupies in relation to its actual weight. Dimensional weight may apply to all shipping company's domestic and international services. Billable weight is the weight used to calculate the rate. For domestic and international services, the billable weight will be the greater of the dimensional weight as compared to actual weight.
Packages that exceed the shipping Company's weight and size limits are not accepted for transportation. If found in the shipping company's system, they are subject to an Over Maximum Limits charge.
How To Measure the Cubic Size of Your Package
Calculate the cubic size of your package by multiplying the height in inches or centimetres (number 1 in the diagram), by the length in inches or centimetres (number 2 in the diagram), by the width in inches or centimetres (number 3 in the diagram). Round each measurement to the nearest whole inch or centimetre. The resulting total is the cubic size of your package.
How To Calculate Dimensional Weight
You can calculate the dimensional weight as the billable weight when the dimensional weight of your package exceeds its actual weight.
Determine Actual Weight: Use any standard scale to determine the actual weight of your package.
Determine Dimensional Weight: Divide the cubic size of your package in inches by 139 to determine the dimensional weight in pounds. Increase any fraction to the next whole pound. For the dimensional weight of your package in kilogrammes, divide the cubic size of your package in centimetres by 5,000. Increase any fraction to the next whole kilogramme.
Determine Billable Weight: Compare each package's actual weight to its dimensional weight. The larger of the two weights is the billable weight and should be used to calculate the rate.
For multiple-package shipments total the billable weight of all packages in the shipment.
For import shipments: Divide the cubic size of your package in inches by 139 to determine the dimensional weight in pounds. Increase any fraction to the next whole pound. For the dimensional weight of your package in kilogrammes, divide the cubic size of your package in centimetres by 5,000. Increase any fraction to the next whole kilogramme.
Using dimensional weight calculations, a freight carrier will charge for lightweight (low density) packages as if they had a greater weight (the weight of the package at the minimum accepted density).
For example, a box of clothing shipped internationally which weighs 10 pounds, and measures 18 x 18 x 18 inches, would be charged as if it weighed 36 pounds: (18 x 18 x 18)/166 = 35.1 pounds which is then rounded up to 36 pounds. This is the weight the package would theoretically weigh if it had a density of 166 in3/lb or 10.4 lb/ft3. (18 x 18 x 18) = 3.375 ft3 x 10.4 lb/ft3 = 35.1 lb.
Keep in mind that there are two different calculations for dim weight. Domestic Shipments: (L x W x H)/166 and International Shipments: (L x W x H)/139
This is the most significant reason.
Shipping costs have historically been calculated on the basis of gross weight in kilograms or pounds. By charging only by weight, lightweight, low density packages become unprofitable for freight carriers due to the amount of space they take up in the truck/aircraft/ship in proportion to their actual weight. The concept of Dimensional Weight has been adopted by the transportation industry worldwide as a uniform means of establishing a minimum charge for the cubic space a package occupies.