The formula
volume (cm³) = length × width × height volumetric (kg) = volume / divisor chargeable (kg) = the larger of actual and volumetric
All dimensions in centimetres. Measure the outside of the packed carton, not the product: the carrier measures what it handles, including the box, the protruding lid and anything taped to the outside.
Irregular shapes are measured at their extremes — a cylinder is billed as the rectangular box it would fit inside, which is why round items ship badly.
Volumetric weight and dimensional weight are the same figure under two names — DIM weight in North American rate cards, volumetric in European ones. Neither is what you pay: what you pay is the chargeable weight, the larger of that figure and the scale.
Worked example
A carton of 60 × 40 × 40 cm weighing 8 kg, sent by express parcel with a divisor of 5000:
- volume = 60 × 40 × 40 = 96,000 cm³ (0.096 m³)
- volumetric weight = 96,000 / 5000 = 19.2 kg
- actual weight = 8 kg
- chargeable weight = 19.2 kg
You pay for 19.2 kg while shipping 8 kg — nearly two and a half times the weight on your scales. Nothing has gone wrong; the box is simply light for its size.
The divisor is really a density threshold
This is the part that makes the whole thing intuitive. A divisor of 5000 means one kilogram is allowed for every 5,000 cm³ — which is 200 kg per cubic metre. Anything less dense than that gets billed on volume; anything denser gets billed on weight.
| Divisor | Billed on volume below |
|---|---|
| 3000 | 333 kg/m³ |
| 4000 | 250 kg/m³ |
| 5000 | 200 kg/m³ |
| 6000 | 167 kg/m³ |
Water is 1000 kg/m³. Almost any packaged consumer product comes in well under 200, which is why volumetric weight decides the bill far more often than sellers expect.
How to lower the chargeable weight
If volume is winning, the only lever is the box.
- Right-size the carton. Volume scales with all three dimensions, so trimming 2 cm from each side of a 30 cm cube removes 19% of the volume, not 7%.
- Watch the third dimension. Height is the one people leave generous, and it costs exactly as much as length.
- Consider one larger box instead of two. Combining removes the duplicated wall thickness and void fill — but check the carrier’s maximum dimensions before you do, since oversize surcharges undo the saving.
- Negotiate the divisor, not just the rate. For consistently bulky goods a better divisor is worth more than a discount per kilogram.
Rounding
Most carriers round the chargeable weight up before pricing — commonly to the next 0.5 kg for parcels and the next full kilogram for air freight. Some round each dimension up to the next whole centimetre first, which compounds slightly.
This calculator shows the exact unrounded figure so you can see where you sit. If you land just above a rounding step, a centimetre off the box may drop you below it.
Frequently asked questions
The higher of the two, always. Carriers call this the chargeable or billable weight. You are never charged the lower figure, and never both.
Because they are selling different kinds of space. Sea freight can afford roughly one tonne per cubic metre; an aircraft cannot. The divisor reflects how tight capacity is on that mode — and within a mode it is a commercial term you can negotiate.
The box, as it leaves your warehouse — outer dimensions, including tape, corner protectors and any pallet if the goods are palletised. The carrier measures what it picks up.
The same way, using the pallet footprint and the total loaded height including the pallet itself. A euro pallet (120 × 80 cm) loaded to 120 cm is 1.152 m³, which at a divisor of 3000 is 384 kg chargeable — often far above the real weight.
It works in centimetres and kilograms, which is what European carriers use. Imperial divisors are different numbers entirely (139 rather than 5000), so mixing the two systems produces nonsense.
There isn’t one. Unlike VAT or duty rates, the divisor is a commercial term, not a published rule — it lives in your carrier contract or rate card. The values here are what each service type typically uses, and the manual field is there because yours may well differ.