Volumetric weight formula
Volumetric weight—also called dimensional weight or DIM weight—converts package volume into a weight-equivalent for rating. With outside dimensions in centimetres, the calculation is length × width × height ÷ dimensional divisor. Multiply the per-package result by quantity only when the packages are identical and the applicable rating rules allow the same treatment.
The divisor matters. A lower divisor creates a higher dimensional weight. ShipMeasure therefore lets you compare 5,000, 6,000 and 4,000 rather than pretending one factor applies to every service. DHL Express UK, FedEx UK and UPS UK currently publish examples based around 5,000 cm³/kg for relevant parcel services; service rules, measurement rounding and contracts can differ.
Worked example: bulky 8 kg carton
A 60 × 40 × 40 cm carton has 96,000 cm³ of volume. At a divisor of 5,000 its dimensional weight is 19.2 kg. If the carton actually weighs 8 kg, size rather than mass is driving the planning chargeable weight.
At a 6,000 divisor the same carton would produce 16.0 kg DIM. That is why the correct carrier/service rule needs to be checked before turning a planning result into a freight quote.
Actual weight, DIM weight and billable weight
Actual weight is what the packed parcel weighs on a scale. Dimensional weight represents the space the parcel consumes. Many parcel carriers rate a package using the higher of those two values, after applying their own measurement and rounding rules. The standalone result above shows the comparison for identical packages; the main Shipment Workspace is preferable for mixed cargo because it calculates the comparison line by line.
Measure the finished package, not the product
DIM calculations are especially sensitive to inaccurate dimensions because all three measurements are multiplied. Measure the outermost packed points and consider bulges, protective packaging and irregular shapes. UPS, for example, tells UK shippers to measure from the longest points and round measurements before calculating dimensional weight. A small dimensional error repeated across many parcels can create a meaningful difference in billed weight.
When reducing carton size can help
If DIM weight exceeds actual weight, packaging design may be a cost lever. That does not mean “make the box smaller at any cost”: product protection, compression, warehouse handling and packing speed still matter. Use the Packaging Efficiency Calculator to find the mathematical break-even volume, then decide whether a practical carton redesign can approach it.
Continue planning the shipment
Shipment Workspace
Enter mixed cargo once and carry the same data through volume, chargeable weight, pallets, containers and freight costing.
Methodology & sources
See the formulas, planning assumptions, source links and review dates behind ShipMeasure.
Packaging efficiency
Find the carton-volume threshold where dimensional weight stops exceeding actual weight.