Overview

Amazon uses product dimensions and volume measurements to classify items into size tiers, which directly determine the fulfillment fees sellers pay for every unit sold through FBA. Getting accurate product dimensions listed in your catalog is essential because incorrect measurements can lead to unexpected fee increases, size tier misclassifications, and even inventory processing delays. This reference guide breaks down how Amazon measures products, calculates volume, and applies those figures to its fee structure.

Key Points / What Sellers Need to Know

• Three dimensions are required — Amazon measures every product by its length, width, and height (in inches for US marketplace), and these measurements include the packaging the item ships in, not just the product itself.
• Volume is calculated as length × width × height — This straightforward formula determines the cubic space your product occupies in Amazon's fulfillment centers, which feeds into both storage fees and shipping cost calculations.
• Dimensional weight may override unit weight — Amazon compares a product's actual unit weight to its dimensional weight (calculated from volume) and uses whichever is greater when determining fulfillment fees.
• Size tiers drive your fee structure — Products are classified into tiers such as Small Standard-Size, Large Standard-Size, Small Oversize, and Large Oversize based on their dimensions and weight, with fees increasing at each tier.
• Amazon may re-measure your products — Fulfillment centers periodically verify product dimensions using their own measurement systems, and these measurements take precedence over what sellers list in their catalog.

How Product Dimensions Are Measured

Amazon measures products in their fully packaged, ready-to-ship state. This means that if your item ships in a box or poly bag, the outer dimensions of that packaging are what count toward your size tier classification. Measurements are taken at the longest, widest, and tallest points of the package, and Amazon rounds dimensions up to the nearest whole inch for size tier determination. Sellers should note that Amazon's Cubiscan machines and manual measurement processes in fulfillment centers serve as the final authority on product dimensions. If there is a discrepancy between what a seller lists and what Amazon measures, the fulfillment center measurement will be used for fee calculations.