Many people who ship items across the country are often upset because of the shipping costs to mail or transport larger packages. Much of this has to do with the size to weight ratio. If a package is overly large, it can take up excess space during shipping. While a cargo carrier can haul a large amount of weight, large packages that weigh very little can take up most of the available space making it less profitable for the transport company.
Size vs Weight
Large packages can make it difficult to fill a cargo hold, especially if they are odd or unconventional sizes and shapes. This makes it harder for the carrier to plan their load. If the larger packages are lighter weight, money would be easily lost if the shipping rate was determined by weight alone. Unless you are sending an item using flat rate shipping, you may be charged for the size of the box instead of the weight. If you are shipping an item that is small, but extremely heavy, flat rate postage and shipping rates are the way to go.
How to Calculate the Difference
If you are unsure of how your package will be charged, use the simple equation to determine which rate is most likely to be used. Multiply the three dimensions of the package (height, width, and depth) and divide the total by 139. If that number is greater than the total weight, it will be used to determine the shipping costs. If you are still unsure of the cost and want to keep your prices low, look into flat rate shipping to see if there is an option for the size and weight of your package.
Knowing how to properly calculate your shipping costs before you drop your package off will save you both time and frustration in the long run.