Because a plane or a container runs out of space long before it runs out of weight allowance. Carriers therefore bill on chargeable weight, which is the greater of what your parcel weighs and what it occupies. A 2 kg box the size of a pillow is billed like a 7 kg box, and no amount of arguing with the tracking page changes that.
Space is the scarce resource, so you pay for whichever you use more of: kilograms or cubic centimetres. If the goods are dense, you pay for weight. If they are light and bulky, you pay for the space.
Express carriers commonly use a divisor of 5000 or 6000 when dimensions are in centimetres; the smaller the divisor, the higher the volumetric weight. Sea freight is normally priced per cubic metre instead, with a minimum charge per shipment. The divisor belongs to the carrier and the route, not to the seller, so treat it as something to confirm rather than assume.
Say you buy a folded fabric storage cube. The product weighs almost nothing, but the seller ships it in a box.
| Step | Value |
|---|---|
| Packed carton size | 40 × 30 × 30 cm |
| Volume | 36,000 cm³ |
| Volumetric weight (divisor 5000) | 36,000 ÷ 5,000 = 7.2 kg |
| Actual weight on the scale | 1.8 kg |
| Chargeable weight | 7.2 kg — you pay for four times what it weighs |
Now shrink the same item: vacuum-packed and shipped in a 30 × 25 × 15 cm carton.
| Step | Value |
|---|---|
| Volume | 11,250 cm³ |
| Volumetric weight (divisor 5000) | 11,250 ÷ 5,000 = 2.25 kg |
| Chargeable weight | 2.25 kg — roughly a third of the freight |
Nothing about the product changed. Only the box did, and the bill moved by about 70%.
An aircraft has a weight limit and a volume limit, and on most parcel routes it hits the volume limit first. A hold full of pillows reaches the door-closed line while still hundreds of kilos under its weight allowance. Charging only by weight would mean the airline flies a full-looking plane at a loss. Volumetric weight is simply the mechanism that prices the space.
Sea freight has the same logic expressed differently: less-than-container load is usually billed per cubic metre, with a minimum, because the container’s floor area and volume are what is being sold.
Buyers talk about “light but bulky” goods. The trade has a name for it: volumetric cargo (also called light or bulky cargo). The other kind is heavy cargo, where the scale decides.
| Type | What decides the price | Typical examples |
|---|---|---|
| Volumetric / light cargo | Size of the packed carton | Duvets and quilts, pillows, fabric storage boxes, pet beds, camping tarps and tents, empty suitcases, plush toys, lampshades |
| Heavy cargo | Weight on the scale | Metal parts, tools, ceramics, books, batteries, cast hardware, glass |
| Balanced cargo | Either, they land close together | Small electronics, phone accessories, cosmetics, eyelash boxes |
This is the reason two orders of the same value can have completely different freight. A box of phone cases weighs little and measures little, so it is cheap to fly. A box of storage cubes of the same value fills a corner of the hold, and you pay for that corner.
The rough shape of the decision:
There is no universal cut-off, because the answer depends on the route, the season and the current rate. Compare two quotes on identical dimensions rather than trusting a rule of thumb. The full cost build-up is laid out in How much does it cost to ship from China?
Volumetric weight belongs in your product choice, not in your shipping checklist. Two products with the same landed goods price can have wildly different margins once freight is applied, and the difference is decided at the moment you pick the product.
More on this in Sourcing from China for small Etsy and Shopify sellers, and on protecting quality before the box closes in How to inspect goods before shipping from China.
Multiply the packed length, width and height in centimetres, then divide by the carrier's divisor. Express carriers commonly use 5000 or 6000, so a box of 40 x 30 x 30 cm gives 36000 divided by 5000, which is 7.2 kg. The divisor is set by the carrier or route, not by the seller, so confirm it before you promise a delivered price.
The greater of the two, often called chargeable weight. If your box weighs 2 kg but its volumetric weight is 7.2 kg, you are billed as if it were 7.2 kg. Air freight and express parcels are priced this way; sea freight is usually priced by cubic metre instead, with a minimum charge per shipment.
Because the dimensions used for the quote were the product dimensions, not the packed carton dimensions. A warehouse adds a carton, filler and tape, and every centimetre of that box counts. Quotes made before packing are estimates; the chargeable weight is only final once the box is sealed and measured.
Compress soft goods, remove retail packaging such as shoe boxes, choose flat-packed or knock-down designs over assembled ones, and use the smallest carton that fits rather than a standard large box. Consolidating several items into one box removes duplicated packing space, but only helps if the combined box is not much larger than the sum of its parts.
Not sure what your carton will cost to ship? Send me the product link and the quantity. I quote goods, freight and my service fee as one figure, and I send you the packed dimensions with a photo before anything is booked — so the number you approved is the number you pay.
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