Why bulky, light packages cost more than they weigh
A truck or plane runs out of space long before it runs out of weight capacity, so carriers bill by whichever is larger: the package's actual scale weight, or a weight computed from its size. That size-based figure is the volumetric (dimensional) weight.
- length, width, height — outer box dimensions in cm
- divisor — cm³ per kg — set by the carrier type you choose above
- billable weight — what you're actually charged for
More detail
Why a divisor exists at all
A styrofoam cooler or a lampshade box takes up a full pallet slot but weighs almost nothing on a scale — if carriers billed by scale weight alone, that space would go nearly free while a small dense box of tools paid full price for less room. The divisor converts a cargo hold's real constraint, volume, into an equivalent weight so both kinds of shipment are priced on the same basis.
Same box, different bill
The divisor you pick changes the answer a lot: a 40×30×20 cm box comes to 4 kg of volumetric weight under the IATA 6000 divisor but 4.8 kg under a courier's 5000 divisor — a 20% jump for the identical parcel, because a smaller divisor makes every cm³ count for more.
Packing tip. Volumetric weight only cares about the outer dimensions of the box, not the item inside — so a snug, well-fitted box (not the next size up 'just in case') can shave real money off an air shipment.
Frequently asked questions
A 40×30×20 cm box weighs 3 kg on a scale — what does an air freight carrier bill me for?
Volumetric weight = (40×30×20) ÷ 6000 = 4 kg under the IATA divisor. Since 4 kg > 3 kg actual weight, the carrier bills the volumetric figure: 4 kg.
Why does DHL charge more than a general air-freight quote for the same box?
Express couriers commonly divide by 5000 instead of IATA's 6000. The same 40×30×20 cm box comes to 4.8 kg volumetric weight at 5000 versus 4 kg at 6000 — about 20% higher for an identical package.
When does actual weight matter more than volumetric weight?
Whenever the parcel is dense relative to its size — a box of books or metal parts often weighs more on the scale than the size formula gives, so the actual weight becomes the billable figure instead.
Is the Korean domestic courier divisor the same as the international air freight one?
By common industry convention, both use 6000 cm³/kg — but individual courier companies can set their own figure, so check the specific carrier's published rate before relying on it. Note that domestic parcel rates in Korea are usually priced by a size (sum of the three sides) and weight bracket table rather than a per-kg rate, so this figure is used to decide which bracket a parcel falls into, not billed directly.