Dimensional weight (or 'dim weight', 'volumetric weight') is a calculated weight based on the parcel's dimensions, used by carriers when the parcel is light but bulky. You're billed on whichever is higher — actual weight or dim weight.
The longer version.
Carriers use dimensional weight to ensure they're paid fairly for parcels that take up space without weighing much — pillow, foam, light packaging materials. The formula is (Length × Width × Height in cm) ÷ a divisor (typically 5,000 for AU domestic and 6,000 for international). The result is your dim weight in kg. Your shipping cost is calculated on whichever is higher: actual weight or dim weight.
Key facts.
AU domestic divisor
5,000 (most carriers — varies)
International divisor
6,000 typical
Worked example
30 × 30 × 30cm box = 27,000 ÷ 5,000 = 5.4kg dim weight
Most common AU carriers using dim weight
Australia Post, StarTrack, Couriers Please, TNT, DHL, FedEx
Why it matters.
- Bulky-light products (pillows, soft toys, packaging) often ship on dim weight not actual weight
- A 200g cushion can ship at 5kg cost if the box is 30cm cubed
- Dim weight is the silent killer of margin in volumetric categories like pet food, gifts, lifestyle
Common pitfalls.
- Quoting carrier rates without checking which divisor they use
- Optimising packaging size only by weight, not box dimensions
- Not tracking dim weight on returns — return parcels are priced on the same logic
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