A Guide to Calculating Volumetric Weight for Air, Sea, and Road Freight
Let’s say that you have two parcels you wish to deliver.
One contains a kilogram of plastic cups, whereas the other contains a kilogram of lead. It’s natural to assume that the cost of shipping each parcel would be the same. After all, they both weigh a kilogram.
However, that’s rarely the case.
Most shipping companies use a concept called volumetric weight to determine how much they charge for shipping a parcel. Here we explain what this concept means and how it applies to road freight, sea freight, and air shipping.
What Is Volumetric Weight in Shipping?
While physical weight refers to the actual weight of your parcel, regardless of its size, volumetric weight is a calculation that takes the parcel’s size into account. Most shippers use it because space is a premium resource in shipping. You may have a parcel that feels like it’s as light as a feather. But if that parcel takes up a lot of room, it’s taking up space that another parcel could use. As a result, shipping your larger parcel means the shipping company can take fewer parcels, meaning they get less money.
Using volumetric weight to calculate how much to charge is how most shipping companies get around this issue.
But there’s a wrinkle in this assumption.
A shipping company uses an equation to calculate volumetric weight. If the result of that equation is higher than the parcel’s physical weight, they’ll charge based on the volumetric weight. But if the physical weight is higher, the shipping company may choose to charge based on that figure.
How to Calculate Volumetric Weight?
There’s a simple volumetric weight formula in shipping you can use to calculate the weight of your package:
(Length x Width x Height) / The Volumetric Weight Constant
Length, width, and height are simple to explain. Use a tape measure on each side of your parcel to get those figures in centimetres before multiplying them together.
The volumetric weight constant is a little more complicated because this constant changes depending on the shipping method you use. In the below examples, we’ll assume a parcel measuring 50 x 150 x 75 cm. We’ll then apply the volumetric weight formula for each shipping method to a parcel of that size to calculate volumetric weight.
How to Calculate Volumetric Weight for Road Freight
As road vehicles are the smallest of the three shipping methods, volumetric weight often comes into play ahead of physical, or gross, weight. In most cases, road freight companies set the volumetric weight constant to 5,000 m3/kg, though some may use 4,000 m3/kg.
Let’s plug the above figures into equations using both constants.
For a volumetric weight constant of 5,000 m3/kg, you get the following result:
(50 x 150 x 75) / 5000 = 112.5 volumetric kilograms.
You’ll get the following result if the constant is set to 4,000 m3/kg:
(50 x 150 x 75) / 4000 = 140. 625 volumetric kilograms
Apply this calculation to your parcel, taking into consideration your different measurements of height, width, and length. If the result for the weight in volumetric kilograms is higher than the parcel’s gross weight, expect to pay based on the former figure. If the gross weight is higher, your road freight company will typically use that number to calculate its chargeable weight.
How to Calculate Volumetric Weight for Air Freight
The volumetric weight formula in shipping changes if you use air shipping, with the carrier usually adjusting its volumetric weight constant to 6,000 m3/kg. This change is good news because a higher constant results in a lower volumetric weight figure.
Here’s the result for the parcel size discussed earlier:
(50 x 150 x 75) / 6000 = 93.75
Again, use the equation and compare the result against the parcel’s gross weight. Whichever figure is higher is the one that your air shipping company will use to charge you.
How to Calculate Volumetric Weight for Sea Freight
Sea freight uses a 1:1 density ratio when calculating volumetric weight, meaning the volumetric constant is 1,000 m3/kg. Applying this figure to the formula gives the following result for the parcel mentioned earlier:
(50 x 150 x 75) / 1000 = 562.50
As you can see, the volumetric weight in sea freight tends to be higher than it is in air or road freight because of the lower volumetric constant. Furthermore, there’s an additional consideration when shipping by sea – the stowage factor.
Any cargo that has a stowage factor above 40 cubic/tons is classified as light goods. If the stowage factor is below 40 cubic/tons, the item falls under the heavy goods category. You may find that your shipping company levies additional charges for heavy goods.
How Do Volumetric and Gross Weight Influence Chargeable Weight?
The chargeable weight is the weight the shipping company uses to determine how much it charges to ship your package. Both volumetric and gross weight can influence this charge because the company has to consider how to most efficiently store the items it ships.
For example, you may have a light package that takes up a lot of room. That package prevents the shipping company from transporting more packages, meaning it makes fewer deliveries with its vehicle. As a result, it’ll use volumetric weight to determine how much it charges to make up for the fact that it’s shipping fewer parcels.
By contrast, it will use gross weight to determine the chargeable weight if you have a small, but heavy, parcel. That’s due to weight affecting the amount of fuel needed to transport the cargo, for which the carrier must account.
Use the Volumetric Weight Formula to Estimate Your Shipping Costs
Using the volumetric weight formula helps you to figure out an approximate fee for shipping your item. Remember to apply the appropriate volumetric constant based on the shipping method you use. Once you have a figure for the volumetric weight, compare it to the parcel’s gross weight. Whichever is higher is the number that most shipping companies will use to determine their charges.
Finally, always read the shipping company’s contract before agreeing to use them. Some companies use different volumetric constants from the standard ones stated in this article, especially for irregular parcels or certain types of cargo.
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