Many sellers calculate 1688 freight by multiplying the product's actual weight by the per-kilogram rate and calling it done. That works for dense, compact goods. For bulky, light items like pillows, decorative lamps, storage baskets, or plastic toys, it is wrong by a wide margin, and the freight bill that lands is based on volumetric weight, not actual weight. The difference can be as large as the product cost itself.
Why carriers do not just charge by actual weight
A carrier earns money by filling truck space or container volume, not only by handling load weight. A parcel that weighs 3 kg but occupies the space of a 10 kg shipment is a losing trade for the carrier, because that air inside cannot be sold to anyone else. So carriers apply a simple rule: charge whichever is higher between actual weight and volumetric weight (also called dimensional weight).
Volumetric weight is calculated from the dimensions of the parcel. The most common formula used in road freight and domestic China express:
Volumetric weight (kg) = Length (cm) x Width (cm) x Height (cm) / 6,000
The divisor 6,000 is standard for road freight and most domestic China express services. Some air freight lanes use 5,000 instead, which pushes volumetric weight even higher. When you get a freight quote, ask which divisor applies. That single number is load-bearing for your cost model.
A real worked example: decorative pillow vs phone case
Two products side by side make the difference clear.
Decorative pillow (bulky, light):
- Packed dimensions: 50 cm x 50 cm x 20 cm
- Actual weight: 0.6 kg
- Volumetric weight: 50 x 50 x 20 / 6,000 = 8.3 kg
- Carrier charges for 8.3 kg
Phone accessory set (compact, denser):
- Packed dimensions: 15 cm x 10 cm x 5 cm
- Actual weight: 0.4 kg
- Volumetric weight: 15 x 10 x 5 / 6,000 = 0.125 kg
- Carrier charges for 0.4 kg
At a freight rate of roughly VND 40,000 per kg, the pillow costs VND 332,000 in freight per unit. The phone accessory costs VND 16,000. But on 1688, the pillow might cost only a few tens of thousands of dong more than the accessory. If you run your margin model on actual weight, you are starting from a number that is off by 8x for the pillow, and the error shows up only after the shipment lands.
Product categories that almost always trigger volumetric billing
Not every category needs this calculation. But several groups will reliably be charged by volume:
- Pillows, cushions, bedding: Large volume, low density. Volumetric weight is typically 5 to 10 times actual weight.
- Decorative lamps, pendant lights: Mostly thin plastic and glass, light, but packaging boxes are large.
- Plastic toys: Hollow forms. A 1 kg toy set can easily occupy 10 kg of volumetric space.
- Storage baskets, organizer boxes: Woven fiber or composite plastic, tall and wide, very low density.
- Hats, shaped fashion accessories: Cannot be compressed during packing without damage.
- Mid-size kitchen appliances: Plastic kettles, mini blenders, tabletop filters often weigh less than they look.
On the other side, small and dense goods like electronics components, metal hardware, tools, and thick cosmetics creams are almost always billed at actual weight. The standard formula still works for those.
How packaging dimensions affect the bill
The dimensions used to calculate freight are the packed carton dimensions, including the box, bubble wrap, and foam inserts, not the bare product size. A small lamp shipped in a large carton to prevent breakage gets billed at the carton size, not the lamp size.
This matters in two directions.
First, when you request a sample or place a first batch, ask the supplier for the shipping carton dimensions, not the product dimensions. Many factories pack pillows and plastic goods in cartons with several extra centimeters on each side for protection. Those centimeters go directly into your freight cost.
Second, for soft goods like pillows and duvets, vacuum compression can cut volumetric weight significantly. A pillow that ships at 8.3 kg volumetric in a standard carton might compress to 2 or 3 kg volumetric in a sealed vacuum bag, which translates to real freight savings per unit. Check that the supplier can do it and that the product recovers its shape properly on arrival.
Building the right cost model for bulky goods
The simplest way to avoid surprises: when you receive a sample, measure the packed carton, calculate volumetric weight, compare it to actual weight, take the higher number, and multiply by the freight rate for your lane.
Many Vietnamese freight agents now have online calculators or rate sheets that handle this automatically. You enter actual weight and dimensions and get back the chargeable weight. If you route through an order-agent service, ask them directly whether the quote is based on actual or volumetric weight and which divisor they use. Do not leave that question open until the shipment is in transit.
When you model margin for a bulky, light SKU, use volumetric weight in your cost build from the start. If the real bill comes in lower, that is a pleasant gap. If you modeled on actual weight and the real bill is higher, you have been selling at a loss from the first order without realizing it.
The margin impact: why bulky goods are unforgiving
A quick illustration. A batch of 100 decorative pillows priced at 45 yuan each on 1688, at around VND 3,600 per yuan (check the current rate when you calculate), with volumetric weight of 8.3 kg and a freight rate of VND 40,000 per kg:
- Product cost per unit: 45 x 3,600 = VND 162,000
- Freight per unit: 8.3 x 40,000 = VND 332,000
- Freight is roughly double the product cost
In this scenario, the product cost is only about one-third of total landed cost before platform fees, ad spend, or order-agent fees are added. If the selling price on the platform does not have enough headroom to absorb that stack, the margin is negative even on a fast-moving product.
This is why bulky, light goods require either a high selling price or a meaningful reduction in volumetric size. It is not impossible to make them work. But the freight math has to be in the cost model from the first day, not discovered after the first shipment.
Bottom line
Freight on 1688 goods is not always charged by actual weight. For bulky, light items, carriers bill by volumetric weight, and the gap can equal or exceed the product cost itself. Before committing to any large, light SKU, measure the packed carton, run the volumetric formula, compare it to actual weight, and build your margin from the higher number. Skipping that step means your profit projection is based on a weight that does not exist.