Freight class matters because it directly affects how much you pay for shipping. Many people focus only on weight, but freight class is just as important. Two shipments with the same weight can have very different shipping costs if their freight classes are different. Freight class is based on four main factors: density, handling, stowability, and liability. Density is the most important. This is why Freight Class Calculator focus mainly on size and weight. Handling refers to how easy or hard the item is to move. Fragile or oddly shaped items cost more to handle. Stowability means how well the item fits with other freight. Liability includes the risk of damage or theft.