Last month a lighting seller in Shenzhen shipped 820 kg of LED panels to Los Angeles on a DDP air rate quoted in dollars per kilogram. The invoice came in at 1,033 kg. Nothing was added: the forwarder had taken the greater of actual weight and volumetric weight, using a divisor of 6,000, and then applied a light-cargo surcharge on top.
The seller had read "per kg" as "per kilogram of my goods" for about a year. On 6.2 cubic metres a month, that reading cost more than the duty did.
The rule nobody puts on the quote
A DDP rate quoted per kilogram is billed on chargeable weight, which is the larger of actual weight and volumetric weight. Volumetric weight is the cubic volume divided by a divisor — 6,000 is common for air, 5,000 is also used, and the number belongs to whoever is quoting. The quote rarely says which one, and that single digit moves the invoice by 20%.
Where it turns against you
The threshold is density. At a divisor of 6,000, cargo denser than about 167 kg per cubic metre is billed on actual weight and the divisor is irrelevant. Below that line you are paying for air, and light cargo — lamps, furniture, toys, cartons of packaging — sits well below it.
| Basis | How it is calculated | For 6.2 CBM at 820 kg | Against actual |
|---|---|---|---|
| Actual weight | Weighbridge | 820 kg | — |
| Volumetric, divisor 6,000 | 6.2 × 1,000,000 ÷ 6,000 | 1,033 kg | +26% |
| Volumetric, divisor 5,000 | 6.2 × 1,000,000 ÷ 5,000 | 1,240 kg | +51% |
| Per cubic metre | 6.2 CBM, quoted as a rate | 6.2 CBM | Separate basis |
What an old hand does before signing
- Ask whether the rate is per actual or per chargeable kilogram, and what divisor is being used. Two questions, one email.
- Calculate density on the packed carton, not on the product. A lamp in a box with foam has a different density from the lamp.
- Below roughly 150 kg per cubic metre, ask for a per-cubic-metre rate or a full container quote. The numbers usually move in your favour.
- Attack the volume before attacking the rate: nesting, flat-pack, and removing void fill can take 6.2 CBM to 5.4 CBM, which is a 13% cut on a volumetric invoice and nothing at all on a weight invoice.
Where per-kg is the right basis
Dense small cargo — hardware, fittings, components — is billed on actual weight and the volumetric question never arises. Coastal freight and consolidated LCL are often quoted per cubic metre for the same reason. The mistake is not choosing one basis; it is not knowing which one your quote used.
How this lands in the landed cost
The billing basis only touches the freight block. Duty is assessed on customs value, and a customs broker reads the invoice, not the waybill, so a volumetric premium does not raise your duty — it simply never shows up as a line you can recover. On a Shenzhen to USA DDP shipment that is the difference between a cost you can argue about and one you cannot see.
A plain note from the desk: any per-kg DDP quote is a per-chargeable-kg quote. Ask for the divisor before you compare two forwarders, because a cheaper rate with a 5,000 divisor can be the more expensive number.
Before the next quote, send us the carton dimensions, the weight per carton and your monthly volume on WhatsApp. We will run actual weight, 6,000, 5,000 and per-cubic-metre side by side, and tell you which basis your cargo actually belongs on.