Let’s look at this in a very practical way. First, a quick correction: USPS, FedEx, or UPS do not automatically lower their shipping prices using a DIM calculator. Instead, the sender or business uses the DIM calculator to determine the weight at which the carrier might charge them. Both FedEx and UPS state that if the DIM weight exceeds the actual weight, the DIM weight becomes the billable weight. Suppose you are shipping goods via UPS within the USA: Your product: Actual weight = 5 lb But the box: 20 × 16 × 12 inches In the FedEx U.S. example, the divisor is 139: 20 × 16 × 12 ÷ 139 = 27.6 lb   So: Actual Weight = 5 lb DIM Weight ≈ 28 lb Billable Weight ≈ 28 lb   In other words, the product weighs only 5 lb, but the package occupies space equivalent to approximately 28 lb. What do you do now? The calculator tells you: You are shipping a 5 lb item, but it is taking up shipping space equivalent to about 28 lb. So, you try changing the packaging. Suppose the new box is:   14 × 12 × 8 inches DIM: 14 × 12 × 8 ÷ 139 = 9.7 lb Now: Actual = 5 lb DIM = approx. 10 lb So, the billable weight would be approximately 10 lb. This is where the savings come in. Suppose the carrier rates are: 28-lb shipment = $30 10-lb shipment = $15 So: Before = $30 Now = $15   Saving = $15 per package If you ship 1,000 packages per month: $15 × 1,000 = $15,000 per month in potential savings. Actual savings won’t always be this high, as rates depend on the destination, service level, surcharges, and your specific carrier contract. FedEx also lists distance, service level, and surcharges as factors influencing shipping costs.