How does a seller determine the precise dimensional weight for a product shipped via FBM, and why is this crucial?

For Fulfillment by Merchant (FBM) shipments, a seller determines the dimensional weight of a product by measuring the length, width, and height of the packaged item in inches, multiplying these dimensions together, and then dividing the result by the dimensional weight divisor specified by the shipping carrier. The dimensional weight divisor is a number used by carriers to calculate shipping costs based on package volume. If the dimensional weight exceeds the actual weight of the package, the carrier will charge based on the dimensional weight. This is crucial because shipping carriers like UPS, FedEx, and USPS use either the actual weight or the dimensional weight, whichever is greater, to calculate shipping charges. Accurately determining dimensional weight prevents unexpected shipping costs, allows for accurate pricing of products including shipping fees for customers, and enables sellers to compare shipping rates from different carriers effectively to find the most cost-effective option. For example, a large but light item might have a higher dimensional weight than its actual weight, resulting in significantly higher shipping costs if not calculated properly.