Why a 400-Gram Order Gets Charged as 800 Grams: Minimum Size and Volumetric Weight

Short answer: a parcel is charged on the larger of its real weight and its box-shaped weight, and a box too small for the sorting line is rejected whatever it weighs. Both rules are physical rather than commercial, which is why they apply before anyone quotes.

The two weights and the divisor

Air capacity is bought by volume, not by kilograms, so a line's pricing has to convert space into weight to compare the two. The conversion everyone uses on China parcel lanes is length by width by height in centimetres divided by 8,000, which gives the dimensional weight in kilograms. A 15 by 4 by 10 centimetre box is 600 cubic centimetres, or 0.075 kg of air-space — so the true scale weight governs. A 30 by 25 by 20 box of the same 400-gram product is 15,000 cubic centimetres, or 1.875 kg, and that is the number the invoice uses.

Some destinations and some lines apply a different divisor; Japanese legs, for instance, are commonly computed on a 9,000 basis with a floor weight applied to light parcels. Nothing here is our invention, and nothing here is fixed across our 50+ channels — the divisor that applies to your carton is confirmed lane by lane and written on the quote.

The middle row is the ordinary failure: a product that fits a small carton is put in a big one because that carton was on the trolley. The bill nearly quadruples and nobody changed the product.

Why a minimum size exists

Parcel machines sort by reading a label on a face of a box. A parcel under roughly ten by fifteen centimetres has no reliable face: the label overhangs, the item falls through diverters, and it ends up in a manual rescue pile that delays the whole wave. That is why lines refuse very small items rather than charge them more. Our answer when a customer's product is a single small unit is to pack it into a compliant outer rather than argue with the machine, and to treat that outer as a packing decision with its own cost line rather than a free favour.

Maximum sizes exist for the same mechanical reason, and irregular shapes — a round tube, a frame, a thing with a handle — get a surcharge because they are handled by hand instead of by line. Awkward cargo is not refused, it is routed. A carton that cannot travel as a parcel — a pallet, a crate, a machine on a skid — comes into the Shenzhen floor, which has the forklift and the container door for it; parcel stock stays on the Dongguan shelving. And when the outbound channel departs Guangdong, the goods have to reach Guangdong first, because a carton landed at a site that cannot feed that lane has to cross the country before it can leave it.

Two clarifications that save arguments later. The chargeable-weight position we put on a proposal is an approximation of what the lane will bill, because the divisor and the band steps are set by the channel and are confirmed lane by lane as contracts move. And the value written on the parcel is a separate field entirely: the declared value follows the sale, never the carton.

How we settle a carton before quoting

1. Measure the packed carton, not the product. Weigh it packed, not bare.
2. Compute both weights and identify which one governs on the candidate lane.
3. Check the lane's minimum and maximum faces, plus any shape surcharge.
4. Test whether a different outer changes the band — sometimes 2 cm of carton height moves a parcel down a whole step.
5. Record the agreed outer as the standard packing instruction, so the pick floor cannot improvise.

Packing questions that come up in onboarding

Can you use my branded box instead of yours?

Yes, and this is normal. You can purchase packaging and send it into the warehouse with your stock, or ask us to procure it and be charged at purchase cost with a handling multiplier applied. Branded outer cartons are fine for delivery to a consumer; where a blind or neutral shipment is required we pack it that way, which is a separate instruction recorded on the order.

Do you add filler to protect the goods?

Where the product needs it. Volume is not free, so the protection decision is made against the chargeable weight it produces, and we would rather show you the arithmetic than quietly absorb it.

The item is under the minimum size. What now?

Two honest options: pack two units together into a compliant outer, which changes the offer rather than the box, or add an outer that meets the lane's face requirement and accept the packing cost. What we will not do is put a sub-minimum parcel on a line and hope.

Is a polybag cheaper than a box?

Usually, on both weight and volume — provided the product survives it and the lane accepts a bag. That is a channel-by-channel and product-by-product answer, so it is confirmed before the first shipment rather than discovered after the third.

The arithmetic, in full

A divisor is only half the story; the other half is which number a lane chooses to divide, and that is the subject of our note on chargeable weight and volumetric divisors on parcel quotes. Mixed-mode shipments raise the same question twice, because air and sea each round differently — see two weight systems, one invoice. Ask us for the divisor on the specific lane and we will put it in writing, since a figure that changes between channels is not a figure at all.

Put the question to us with your own numbers. FulfillDock by SBT has moved China-origin ecommerce goods since 2011 from three staffed sites — Shenzhen, Dongguan and Suzhou, 24,000 m² of warehouse between them — and the pre-sales modelling behind any answer above costs nothing. Write to Tony Zhang at tonyfulfill@gmail.com or reach him on WhatsApp at +86 186 6591 6878. Our receiving standards sit on the quality page, the company record on About us, and how order data is handled in the privacy notice. Project cargo and traditional B2B freight run through our sister brand, FulfillNexa by SBT (www.fulfillnexa.com).