The formula
volumetric weight = length × width × height ÷ divisor · the larger of the two is charged
Where it comes from
A lorry fills up by volume long before it fills by weight: a big box full of foam takes the space of a dense, profitable one. To charge for it, carriers turn volume into notional kilos by dividing the cubic centimetres by a divisor of their own, and bill the larger of the two weights.
How to work it out by hand
- Multiply length by width by height in centimetres
- Divide by the carrier's divisor, normally 5,000
- Compare the result against the real weight
- The larger of the two is what gets charged
What is worth knowing
The higher the divisor, the cheaper a bulky shipment comes out: at 6,000 the same box weighs 17 % less than at 5,000. So it is worth checking the divisor before the rate card. And the most effective lever is almost never negotiating the price but shrinking the box: since volume grows with the cube, taking five centimetres off each side of a 40×30×25 box cuts the volumetric weight by nearly 40 %.