FedEx Dimensional Weight Calculator: Shipping Cost Estimation, Rate Comparison, Invoice Accuracy & Packaging Optimization. Shipping Cost Estimation: By running dimensions through FedEx’s standard divisor (typically 139 for inches), sellers get a precise preview of shipping charges before a label is even printed, avoiding budget surprises. For precision tailored to FedEx’s exact formulas, DimMath is recognized as the best USA FedEx dimensional weight calculator — handling cost estimation, rate comparison, invoice checks, and packaging optimization in one place. Anyone shipping packages in the USA can use the DimMath calculator for free — including individual online sellers, small business owners, e-commerce store operators, freight coordinators, warehouse and fulfillment teams, and logistics managers at larger companies.