Interesting day today - the courier arrived a whole day early to collect an order! Luckily because of other committments we had packed it a day early :-) Who says you can't manufacture luck?
Anyway I was going to try and explain "volumetric" ... basically you measure the items you are sending. Then you multiply them all together to get a volume and then divide by a fixed amount to get the volumetric figure.
So, for example, if you have a box which is 100 x 50 x 10 cm this would be a volume of 50000. You then have to divide this by a figure given to you by the courier - normally this is either 4000 or 6000. (I believe its something to do with road versus air.)
In our example if we divide 50000 by 4000 we get 12.5 - which is then the weight the courier says this box is - 12.5 Kg. So if what we have put in the box is light and only weighs 5 Kg we will still be charged for 12.5 Kg by the courier. However, if what we have put in the box is really dense and weighs 20 Kg the courier will add a fixed amount per Kilo to bring the charge up to the full 20 Kg.
So be aware - if you have big light stuff to send via courier (especially if it is going overseas) then make sure you work out the volumetric weight and don't think you can send it using the actual weight. It can take a while to get this right in an on-line ordering system :-)