Shipping Cost Calculator: Uses, Comparing Courier Rates, E-Commerce Checkout Integration, Budgeting, Volumetric Weight & Service Level Selection. E-Commerce Checkout Integration: Online stores plug shipping calculators into checkout flows so customers see accurate, real-time shipping costs at the point of purchase — reducing cart abandonment caused by unexpected fees. 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.