Unfortunately, nothing in logistics is simple, especially where couriers are concerned. We at Hutch wish for a world where all the couriers in the world come together and agree on one unified and simple way of doing things. We understand this is a farfetched vision, but one can only dream, eh?
Each courier has their own way of deciding how much they charge you for a shipment, but mostly, they can be broken out into two different ways: dead weight or volumetric weight.
Deadweight - This is the parcel's exact weight captured by the scale, irrespective of its shape and size. This includes the items in the parcel and the box and materials it gets shipped in.
Volumetric weight - This is calculated using the shipment's dimensions, i.e. length, depth and height of the shipment box or mailer bag or envelope etc. and then divided by 5000 or 6000 depending on the courier and the service. Weight is not factored in here.
Traditionally, dead weight was how individuals and companies were charged for shipments. The industry then collectively introduced the concept of volumetric weight, which was believed to be a more accurate estimate of the true shipping cost. At some point, what became most important in the industry was the physical amount of space (volume) a parcel took up on a lorry, van, aircraft, container, etc., not how much it weighed.
In the UK, dead weight is typically used for domestic parcels, whilst volumetric is often used internationally. Volumetric weight is almost always more expensive than deadweight, and most couriers will present both and charge whichever's greater.