How to calculate dimensional weight
Dimensional weight turns a parcel’s volume into a weight figure. Start with the finished outer measurements, multiply the three sides, and divide by the factor for your service. Compare that result with the weight of the complete parcel on a scale.
Planning chargeable weight = max(actual weight, dimensional weight)
Worked example: a 40 × 30 × 20 cm parcel
The volume is 24,000 cm³. With a divisor of 5,000, dimensional weight is 4.8 kg. If the packed parcel weighs 2 kg, the higher figure is 4.8 kg. Selecting whole-unit weight rounding changes that estimate to 5 kg. This example is arithmetic, not a quote for a particular service.
Choose the right units and factor
Use cm³/kg with centimetres and kilograms, or in³/lb with inches and pounds. Switching units converts your measurements, scale weight and divisor together so the raw physical estimate stays equivalent. If your carrier publishes a different factor, replace the converted factor with that exact number.
For context, DHL UK’s weight and dimensions guidance shows a 5,000 divisor for centimetres. UPS US’s dimensions guidance distinguishes a 139 Daily Rates divisor from 166 for Retail Rates in inches. These are service-specific examples, not universal settings. Sources checked 17 September 2026.
What this estimate leaves out
The calculator uses dimensions exactly as entered. It does not apply a carrier’s measurement rounding, minimum chargeable weight, oversize rules, packaging restrictions, destination pricing or surcharges. The weight-rounding option rounds each weight upward before comparison; choose it only if it matches your service. Always obtain a current carrier quote before buying postage.
Common questions
Should I weigh the product or the whole parcel?
Weigh the complete package, including the box, cushioning, tape, labels and any inserts. A product-only weight understates the shipment.
Can I use a divisor of 6,000?
Yes. Enter the factor supplied by your carrier or forwarder. The tool accepts a positive custom factor; the default does not establish which rule applies to your account.
Is a lower dimensional weight always cheaper?
No. The actual weight can remain higher, and rate bands or surcharges can still determine the price. Compare actual quotes for both packed sizes.
Next: understand actual versus dimensional weight, or measure a finished parcel consistently.