The basic calculation
Actual weight is what the package physically weighs. Dimensional weight is calculated from the space the package occupies. Many shipping services compare the two when rating a package.
Compare actual weight with calculated DIM weightWorked example
If a package weighs 12 kg but its dimensional weight is 16.8 kg, the dimensional value is the larger comparison value. The carrier may then apply its own billing and rounding rules.
What to check before using the result
Reducing empty space can sometimes reduce dimensional weight. Recheck package dimensions after final packing rather than relying on the product carton specification alone.
Use the result as part of shipment preparation, then keep the final dimensions, weights and package counts consistent with the packing list, carrier instructions and other paperwork.
Reminder: Carrier measurement, rounding, classification and billing rules vary. Confirm the rules that apply to your shipment.